William S. Furneaux

We now pass from the animal to the vegetable kingdom, our object being to give a general outline of the nature and distribution of the principal marine algÆ or sea weeds that grow on our shores; and to supply a brief account of those flowering plants that either exhibit a partiality for the neighbourhood of the sea, or that grow exclusively on the rocks and cliffs of the coast. The present chapter will be devoted to the sea weeds themselves, but we consider it advisable to precede our account of these beautiful and interesting plants by a brief outline of the general classification of plant-life, in order that the reader may be able to understand the true position of both these and the flowering plants in the scale of vegetable life.

Plants are divided into two great groups, the Cryptogams or Flowerless Plants and the Phanerogams or Flowering Plants. In the former the reproductive organs are not true seeds containing an embryo of the future plant, but mere cells or spores, which give rise directly to a thread or mass of threads, to a cellular membrane, or to a cellular body of more or less complexity of form from which the flowerless plant is afterwards developed; while in the latter the reproductive organs are flowers that give rise to true seeds, each of which contains the embryo plant.

The Cryptogams are subdivided into four groups—the Thallophytes, the Charales, the MuscineÆ, and the Vascular Cryptogams.

The first of these includes all the very low forms of vegetable life, the simplest of which (Protophyta) are minute plants, each consisting of a single microscopic cell that multiplies by a process of budding, no sexual organs of any kind being produced. Some of these minute unicellular organisms contain chlorophyll—the green colouring matter of plants, by the action of which, under the influence of light, the plant is enabled to decompose the carbonic acid gas of the atmosphere, using the carbon for the purpose of building up its own substance, and setting free the oxygen into the air again. Others contain no chlorophyll; and these, having no power of feeding on carbonic acid gas, are more or less dependent on organic matter for their supplies of carbon.

Only very slightly removed from these minute plants are the AlgÆ of fresh and salt water, varying in size from microscopic dimensions to enormous plants, the lengths of which may reach many yards and the weight several stone. They contain chlorophyll, and can therefore avail themselves of inorganic food material; and although some multiply only by repeated subdivision of their cells, others develop sexual organs by the union of which fertilised spores are formed. The nature of these AlgÆ will be more fully described presently; and we will go no further now than to justify the location of such large and conspicuous plants (as many are) so low in the scale of vegetable life by stating that they are entirely cellular in structure, never producing true vessels such as we see in higher plants; and that though some of them develop parts which more or less resemble the leaves and roots of higher forms, the former are far more simple in structure and function than true leaves and the latter are never engaged in the absorption of food from the soil to which they are fixed.

Another important group of the Thallophytes is formed by the Fungi, which include the familiar mushrooms, toadstools, and the sap-balls so commonly seen on decaying trees; also the smaller forms known as moulds, mildew, and smut. These, also, are entirely cellular in structure; and, since they develop no chlorophyll, are compelled to live as parasites on living beings or to derive their food from decaying organic matter. Thus they are the creatures of corruption, their presence always denoting the breaking down of living matter or of matter that has previously lived.

Now leaving the Thallophytes, and passing over the small group of aquatic plants known as the Charales, we come to the MuscineÆ, which contains the Liverworts (HepaticÆ) and the Mosses (Musci).

The plants of both these groups require much moisture, and are found principally in damp, shady situations. Like the preceding groups they are cellular in structure, never producing true vascular bundles such as the higher plants possess; and their life histories are rendered interesting by the ‘alternation of generations’ which they exhibit. The first generation is a sexual one produced from the spores, and consists either of a mass of delicate threads from which a plant with a leafy axis is developed by a process of budding, or of a little green frond (the thallus). These bear the male and female elements, called respectively the antheridia and the archegonia; and when the central cells of the latter are fertilised by the former, they give rise to a case, with or without a stalk, containing a number of spores. When the case is ripe, it opens horizontally by means of a lid, thus liberating the spores.

Following these in the ascending scale are the Vascular Cryptogams, in which some of the cells become modified into true vessels. Here, too, the plants exhibit a distinct alternation of generations, the spore first giving rise to a small, leafless body, the prothallium, which bears the sexual organs; and then the female elements, after fertilisation, produce the spore-bearing plant.

This group contains quite a variety of beautiful and interesting plants, including the Ferns (Filicales), Horsetails (Equisetales), Club-mosses (Lycopodiales), Water Ferns (RhizocarpeÆ), and Selaginellales.

Ferns usually produce their little green prothallia above ground, and the perfect plant generally has a creeping rhizome or underground stem. Some, however, have strong, erect, woody stems, such as we see in the tree ferns of tropical and sub-tropical countries. The horsetails and the club-mosses are also produced from prothallia that are formed above ground. The perfect plants of the former have branching underground stems which give off numerous roots, and send up annually green, jointed, aËrial stems that bear whorls of fine leaves, each whorl forming a toothed, ring-like sheath. The fertile shoots terminate in cones, on the modified leaves of which the sporangia are produced. The stems of the club-mosses are clothed with small overlapping leaves, in the axes of which the sporangia are produced; and the spores, which are formed in abundance, constitute the lycopodium powder with which druggists often coat their pills.

Water ferns either float on the surface of water or creep along the bottom, and produce their fruit either at the bases of the leaves or between the fibres of submerged leaves. The Selaginellas are characterised by a procumbent stem that branches in one plane only, producing small, sessile leaves, with a single central vein. A number of roots grow downward from the under side of the stem, and the fruit is developed in the axils of the leaves that form the terminal cones of the fertile branches.

The above are all the principal divisions of the flowerless plants, and we have now to note the general characteristics of the Phanerogams. The chief of these is, of course, the possession of flowers as reproductive organs; and although it is not convenient to give a full description of the flower at the present time, it will be necessary to say a little concerning it in order that we may be able to grasp the broad principles of classification.

A flower, in its most complex form, consists of parts arranged in four whorls arranged concentrically. The first and second whorls, commencing from the outside, usually consist of leaf-like bodies, united or distinct, and are called respectively the calyx and the corolla. The third whorl consists of stamens, which are the male reproductive organs of the plant, and each stamen consists essentially of a case—the anther—in which are formed a number of little pollen cells. When the anther is ripe it opens, thus liberating the pollen, so that it may be dispersed by insects, by the wind, or by other mechanical means. The remaining whorl constitutes the pistil, which is generally made up of parts (carpels) arranged round a common centre, and each surmounted by a stigma adapted for the reception of the pollen cells. This portion of the flower contains the ovules, enclosed in a case called the ovary, and is, therefore, the female organ of the plant. When the ovules have been fertilised by the pollen, they develop into seeds, each one of which contains an embryo plant; and the ovary itself, ripening at the same time, develops into the fruit.

Such is the general description of a flower in its most complex form, but it must be remembered that one or more of the whorls named above may often be absent. Thus, calyx or corolla, or both, may not exist; and the male and female organs may be developed on separate flowers of the same plant, or even, as is frequently the case, on different plants of the same species. In the latter instance the flowers are spoken of as unisexual, those bearing the stamens being the staminate or male flowers, and those bearing the pistil the pistillate or female flowers.

The Phanerogams are divided into two main groups, the Gymnosperms and the Angiosperms. In the former the ovules are naked, no ovary or seed-case being developed. The pollen, carried by the wind, falls directly on the ovule, and then develops a tube which penetrates to the nucleus of the ovule, thus fertilising it. In the Angiosperms the ovules are always enclosed in an ovary, and the pollen grains, alighting on the stigma, are held by a gummy secretion. The tubes they produce then penetrate through the underlying tissues, and thus come into contact with the ovules.

The Gymnosperms include a group of small palm-like trees and shrubs (the CycadeÆ), of which the so-called Sago Palm is a representative; and the ConiferÆ or cone-bearing shrubs and trees, which may be spoken of collectively as the Pines. In the latter the leaves are either stiff, linear, and needle-like, or short and scale-like, or are divided into narrow lobes; and the plants are noted for their resinous secretions. The flowers are always unisexual, and are generally arranged in cylindrical or short catkins, where they are protected by closely packed scales; but the female flowers may be solitary. There is no calyx or corolla, but the naked ovules and seeds are sometimes more or less enclosed in the scales (bracts) or in a fleshy disc.

The Angiosperms form the highest division of the flowering plants; and are subdivided into two extensive groups—the Monocotyledons and the Dicotyledons. The chief distinguishing feature of these is that implied in the above names, the embryo of the former containing but one rudimentary leaf (cotyledon), while that of the latter contains two. The Monocotyledons are also characterised by having the bundles of vessels (vascular bundles) of the stems dispersed; the veins of the leaves are also usually parallel, and the parts of the flower are arranged in whorls of three or six. In the Dicotyledons the vascular bundles of the stem are united into a ring which surrounds a central pith; the veins of the leaves form a network, and the parts of the flower are arranged in whorls of four or five.

We are now enabled to understand the relative positions of the principal groups of plants in the scale of vegetable life, and to locate approximately the forms with which we have to deal; and to aid the reader in this portion of his work we present a brief summary of the classification of plants in the form of a table for reference:—

THE CLASSIFICATION OF PLANTS

I. CRYPTOGAMIA—Flowerless plants.

(a) THALLOPHYTES—Leafless, cellular plants.

1. Protophyta—Unicellular plants.

2. AlgÆ—Sea weeds, &c.

3. Fungi—Mushrooms, &c.

(b) CHARALES.

(c) MUSCINEÆ.

1. HepaticÆ—Liverworts.

2. Musci—Mosses.

(d) VASCULAR CRYPTOGAMS.

1. Filicales—Ferns.

2. Equisetales—Horsetails.

3. Lycopodiales—Club-mosses.

4. RhizocarpeÆ—Water ferns.

5. Selaginellales.

II. PHANEROGAMIA.

(a) GYMNOSPERMIA.

1. CycadeÆ—Cycads.

2. ConiferÆ—Cone-bearing trees.

b) ANGIOSPERMS.

1. Monocotyledons.

2. Dicotyledons.

We have now to deal more particularly with those marine AlgÆ that are commonly known as Sea Weeds, and which add so much to the beauty of our rocky coasts. These exhibit such a variety of graceful forms, and such charming colours, that they are admired and treasured by thousands of sea-side ramblers, who are attracted by them merely on account of their pleasing general appearance; but the naturalist has all this and a great deal more to interest and instruct him, for the sea weeds possess quite a number of peculiar and characteristic features that render them well worthy of a detailed study, especially when they are compared and contrasted with the better-known flowering plants of our fields, woods, and hedgerows.

It has already been observed that sea weeds differ from the majority of flowering plants in that they have no true roots or leaves, though they are often attached to rocks and other substances by a root-like disc, and sometimes have leaf-like expansions that are supported by stem-like rods. The root-like structures, however, serve simply for the attachment of the plant, and are never concerned in the absorption of nourishment like the true roots of higher plants; and the leaf-like expansions, though they are sometimes symmetrical in form, never exhibit the spiral arrangement that obtains in the leaves of higher plants, from which they also differ in function.The plant-body of a sea weed is called a thallus, and differs considerably in the various species. Sometimes it has no expanded portion whatever, but is more or less cylindrical in all parts, and may be either branched or simple; and in some species it forms a simple crust or a soft jelly-like covering on a rock.

All portions of a sea weed are made up of cells, and these are never modified into vessels such as we see in the stems, leaves, and roots of higher forms of vegetable life; and one who is commencing the study of the algÆ will find much interesting work in the examination of their microscopic structure. Thin sections of various parts of the larger weeds, cut with a sharp knife or a razor, and examined in a drop of water under a cover-glass, will show the cellular structure perfectly; while minute fragments of the small and slender species are sufficiently thin and transparent to display the form and arrangement of their cells without any previous preparation.

One of the principal charms of the marine algÆ lies in the great variety of colour that they display. They all contain chlorophyll—that remarkable green colouring matter which enables a plant, under the influence of light, to feed on the carbonic acid gas existing in the atmosphere, or held in solution in water; and with its aid the sea weeds can utilise this product of decay and animal respiration that would otherwise accumulate in the water of the sea. But, in addition to this bright green chlorophyll, many of the sea weeds contain a second colouring substance, and in these the great variety of tint is dependent on the nature of the latter and on the proportion in which it is present as compared with the chlorophyll itself.

The different means by which the algÆ reproduce their kind forms a most engrossing subject, and to the botanist a most important one, for it has much to do with the classification of the species. The affinities of plants may be better determined by the nature of their reproductive processes than by any other features, but unfortunately this is not so well understood with regard to the algÆ generally as compared with many other divisions of the vegetable kingdom; and, as a consequence, there is still a considerable difference of opinion, not only as to the extent of the whole group, but also as to its divisions and subdivisions. The reason for this is clear; for while it is quite an easy matter to trace a flowering plant through its complete cycle from seed to seed, it requires a much more careful examination, combined with much microscopic work, to trace a lowly organised plant from spore to spore.Some of the algÆ may be reproduced without the agency of any sexual elements; that is, without the aid of parts that correspond with the ovules and the fertilising pollen of a flowering plant. Some of these are reproduced by a repeated subdivision, or by the separation of a portion of the plant that is capable of independent growth; while others produce spores that do not result from the fusion of two different cells. In most, however, sexual differences are to be observed, some cells being modified into female organs, containing one or two more minute bodies that are capable of developing into new plants after they have been fertilised, and other cells produce the male elements by means of which the fertilisation is accomplished. The fertilised cells are spores, but are named differently according to the nature of their development. They all differ from true seeds in that they never contain an embryo plant, but germinate by the elongation of some particular part, which subsequently grows by a continuous process of cell-division; or the cell-division may originate directly in the spore without any previous elongation or expansion.

The sea weeds are usually classified according to the colour of their spores; but, since this colour generally corresponds with that of the plant itself, we may almost say that they are grouped according to their general tints. There are three main divisions:—

The ChlorospermeÆ, or Green-spored;
The RhodospermeÆ, or Red-spored; and
The MelanospermeÆ, or Brown-spored.

The ChlorospermeÆ contain no colouring matter other than the chlorophyll. They are mostly small weeds, of a delicate green colour; and, although they are not particularly conspicuous on our shores, they contribute very considerably to the beauty of the rock pools, where their delicate green fronds contrast richly with the olive Melanosperms and the pink and white corallines. The thallus or plant-body is very varied in form, sometimes consisting of a broad membrane, but more commonly of tufts of slender green filaments or of narrow, flattened fronds.

These weeds are most beautiful objects for the microscope, and they are generally so thin and transparent that no section-cutting is necessary, nothing being required except to mount very small portions in a drop of water. In this simple manner we may study the beautiful arrangement and the various forms of the cells of which they are composed. The more delicate species will be found to consist of a single layer of cells only, while in the larger forms—the UlvaceÆ, for example—the thallus may be formed of two or three distinct layers, and some of the cells may be elongated into tubes.

A remarkable feature of the green-spored weeds is the large size of the chlorophyll granules as compared with those of the other groups, and also the great variety of forms which these granules assume. They may be easily seen under a low power, and the examination of the weeds will show that the thalli are not uniformly green, but that the colour of the plants is due entirely to the chlorophyll granules, the remainder of the plant substance being quite colourless.

If a green sea weed be placed in alcohol for a short time, it will be found that the liquid assumes a green colour, while the plant itself becomes colourless. The explanation is, of course, that chlorophyll is soluble in alcohol. The presence of starch also in the weed may be proved in a very simple manner, as follows:—Mount a small piece in water, and then put a drop of iodine solution by the edge of the cover-glass. The solution will gradually diffuse itself around the object, turning the starch-grains to a deep blue colour, and so rendering them very conspicuous under a moderately high power.

The manner in which the green weeds are reproduced is very interesting also. In some cases the fragments of a thallus that have been detached by storms or other mechanical means possess the power of independent growth, and develop into plants; and this mode of reproduction may often be watched in the indoor aquarium. Another method is by the agency of little spores (zoospores) that are produced at the edges or extremities of the thallus. Certain of the cells become modified into what are called zoosporangia, and the minute zoospores are formed within them. The walls of the cells either gradually degenerate, or are fractured, and the zoospores are thus set free. The latter are provided with little vibratile cilia, by which they move about freely in the water. Some eventually settle down and germinate without any further aid, but others are unable to develop until they have been fertilised by fusion with another cell. The former is therefore an asexual development, while the latter is sexual.

Some of the delicate, filamentous green algÆ are reproduced by another process termed conjugation. In this case two adjacent threads that lie close together become lightly united by a covering of gelatinous substance, and a cell of each throws out a process. The processes are directed towards each other, and unite to form a tube in which the contents of the two cells become fused together, with the result that zoospores are produced.

Among the lowest of the green sea weeds are the plants known collectively as the ConfervaceÆ, which consist of delicate green filaments, usually attached to rocks in dense masses, but often found floating freely in the rock pools. The filaments are composed of cells joined together at their ends, and are always unbranched.

ConfervÆ are found principally in the tide pools, especially near high-water mark, and often abound in hollows in the rock even above high-water mark, where the spray of the waves is mingled with rain-water or the drainage from the land. They exist in both fresh and salt water, and some species seem capable of thriving in brackish water of any degree of salinity.

Allied to the confervÆ is a group of marine algÆ called Cladophora, very similar to the former in general appearance, and found in similar situations, but readily distinguished by the branching of their jointed filaments. The various species of this group are very beautiful weeds, their delicate filaments looking very pretty as they float and sway in the water of the pools. They are also exquisite objects for the microscope; but, unfortunately, often lose their natural colour when preserved dry. They vary in colour, some few being of a dull green tint, while others are bright green, sometimes with a beautiful silky gloss.

One species (C. pellucida) is more rigid than most of the others; its fronds stand out erect and firm, and are repeatedly forked near the tips. It is a moderately common weed, found in the lower rock pools, and may be readily recognised by the long one-celled joints, from the tops of which the branches proceed. Another species (C. diffusa) is also very firm in structure, so much so that its bristly tufts retain their form when removed from the water, instead of becoming matted together in a shapeless mass. Its branches are rather long, and bear a few simple branchlets towards their extremities. It is found in rock pools between the tide-marks. C. lanosa is a very pretty little weed, growing in dense globular woolly tufts, an inch or more in diameter, on the olive tangles between the tide-marks. It is of a pale yellowish-green colour, which becomes much paler, or is even altogether lost, when the plant is preserved in a dry state, and, at the same time its fine glossy appearance is lost. Its fronds have straight branches, all making very acute angles, and they have also small root-like filaments. It much resembles another species (C. arcta), which grows in dense tufts on rocks, but the latter is larger, not so slender, and more freely branched. The cells, too, of C. arcta are longer, being about ten times the length of the diameter, and the fronds are silvery at the tips.

Nearly thirty species of Cladophora have been described, but it is impossible to give here a detailed description of all. We add, however, a brief summary of the distinguishing features of a few other species that are common on our coasts.

C. rupestris is common everywhere, and easily recognised by its rigid, branching, tufted fronds, of a dark greyish-green colour; its branches, which are opposite, bear awl-shaped branchlets. It is found in rock pools from half-tide downwards, and in deep water beyond the tide-marks, the plants growing in the latter situations being generally of a fine dark-green colour.

C. lÆtevirens is also very common on rocks between the tide-marks. Its fronds are tufted and freely branched, of a pale-green colour and soft flexible texture, and about six inches long. The branchlets are usually slightly curved.

C. gracilis is a beautiful plant that grows on large weeds, especially the Sea Grass (Zostera) in deep water; and although not very common, it is sometimes found on the beach after storms. It is characterised by its slender silky fronds, from a few inches to a foot in length, of a yellowish-green colour. It may always be known by the comb-like branchlets growing only on one side of each branch.

C. refracta grows in dense tufts, two or three inches long, in rock pools near low-water mark. Its fronds consist of rigid stems in rope-like bundles that are very freely branched, the whole tuft being of a yellow-green colour and silky texture. C. albida closely resembles it in structure and habit, but may be distinguished by its paler colour, which disappears when the weed is dried, and by its longer and more delicate branches.

In another order of the green-spored algÆ (the SiphoneÆ or SiphonaceÆ) the frond is formed of single branching cells, and many of these are often interwoven into a spongy mass, and sometimes coated with a deposit of calcareous matter.

In the genus Codium the fronds are of a sponge-like texture, composed of interwoven branching fibres, and are of a globular, cylindrical, or flattened form. The commonest species is C. tomentosum (Plate VII.), which consists of sponge-like, dark-green cylindrical fronds, which are forked and covered with short hairs that give it a woolly appearance when in the water. Each frond is composed of slender interwoven fibres with club-shaped filaments passing vertically to the surface. It grows on rocks in the pools between the tide-marks, and is abundant on nearly all our coasts.

The Purse Codium (C. bursa) has spongy hollow fronds of a globular form, varying from a quarter of an inch to five or six inches in diameter. It is a rare species, being found only at a few places on the south coast. Another species (C. adhÆrens) adheres to rocks, over which the fronds spread in irregular soft patches, the club-shaped vertical filaments of its interwoven fibres giving it the appearance of rich green velvet.

An allied weed (Bryopsis), named from its moss-like appearance, grows in erect tufts, each frond consisting of a branched one-celled filament. There are two species of the genus, one (B. plumosa) characterised by the light feathery nature of its fronds, the stems of which are branched only near the top. It is found in rock pools on most of our coasts. The other (B. hypnoides) is more freely branched, and the branches are long, and issue from all sides of the stem. Like the last species, it has branches on the outer part of the stem only, but it is of a softer texture.

The best known of the green-spored weeds are certainly those belonging to the UlvaceÆ, characterised by their flat or tubular fronds, sometimes of a purplish colour, the cells of which multiply both horizontally and vertically as the plants grow. In the typical genus, Ulva, the frond is sometimes in two distinct layers, and becomes more or less inflated by the accumulation of either water or oxygen between them. The commonest species are U. lactuca and U. latissima, both of which are eaten by the dwellers on some of our coasts. The former, commonly known as the Lettuce Ulva, has a frond of a single layer of cells, and grows on rocks and weeds between the tide-marks. It is common on many oyster beds, and is employed by the fishermen to cover the oysters when sent to market; they call it ‘oyster green.’ This species is shown on Plate VIII. U. latissima or the Broad Ulva sometimes reaches a length of two feet, and a breadth of nearly a foot. The fronds are composed of two layers of cells, are of an irregular shape, with a very wavy, broken margin, and of a bluish-green colour, It is known as the Green Laver, and is used as food in districts where the true laver (Porphyra) is not to be obtained. A third species—the Narrow Ulva (U. Linza)—has smaller and narrower fronds, of a more regular shape and of a bright-green colour. The fronds are composed of two layers of cells.

Plate VII.

SEA-WEEDS

1. Fucus nodosus	3. Codium tomentosum
2. Nitophyllum laceratum	4. Padina pavonia
5. Porphyra laciniata

The UlvÆ retain their colour perfectly when dried, and, with the exception of U. latissima, are of a mucilaginous nature, and adhere well to paper, but, unfortunately, the graceful wavy outline of the fronds is lost in pressed specimens.

The ‘true laver’ mentioned above, which is also popularly known as Sloke, is closely allied to Ulva, but may be distinguished from it by the colour of its membranous fronds, which vary from a light rose to a deep purple or violet, occasionally inclining to olive, but never green. Its scientific name is Porphyra laciniata (Plate VII.), and it differs from the majority of the chlorospermeÆ in having dark-purple spores, which are arranged in groups of four in all parts of the frond. The fronds are very variable in form and size, being sometimes ribbon-like, and sometimes spreading into an irregular sheet of deeply-divided segments; and the remarkable variety of form and colour has led to a division into several species. These, however, merge into one another so gradually that the separation seems to be hardly necessary.

The same remark concerning the multiplicity of species applies to another allied genus called Enteromorpha, in which the fronds are green and tubular, and often more or less branched. In these the colour varies from a pale to a dark green, and the cells are arranged in such a manner as to give a reticulated appearance. The commonest and best-defined species are E. intestinalis, the tubular fronds of which are constricted at intervals in such a manner as to resemble the intestines of an animal, and E. compressa, with branched fronds of variable form and size. The former is common on all our coasts, and may even be found in rivers and ditches some distance from the sea. It thrives equally well in fresh and salt water, and appears to grow most luxuriantly in the brackish waters of tidal rivers. The latter species also thrives best in similar situations.

Coming now to the red-spored sea weeds (RhodospermeÆ), we have to deal with some of the most charming of the marine algÆ that invariably attract the sea-side rambler, and provide many of the most delightful objects in the album of the young collector. Their brilliant colours, varying from a light red to dark purple and violet, are sufficient in themselves to render them popular with the collector, but in addition to this striking feature they are characterised by extreme elegance of form and delicacy of texture. They are to be found in most rock pools, from near high-water mark downwards, the smaller and more delicate forms adding much to the beauty of these miniature seas; but the largest and many of the prettiest species exist only at or beyond the lowest ebb of the tide, and hence the algologist, in quest of these beautiful plants, will find it necessary to work at the very lowest spring tides, with the occasional aid of a small boat drifted into the narrow channels among outlying rocks, and a long hook with which to haul up submerged specimens; and it will also be advisable to search the line of dÉbris at high-water mark after stormy weather for rare weeds that may have been detached and washed ashore by the angry waves.

While engaged in the former of these employments—the searching of outlying rocks with the boat—and also when examining the outer rock pools which are disturbed by the waves that wash over their banks, the simple instrument known as the water-telescope will prove invaluable. Everyone must have noticed how difficult it is to observe objects in water, the surface of which is disturbed by the wind or some other cause; but the simple appliance named, consisting only of a long tube of metal, a few inches in diameter, and painted a dead black inside, will enable the observer to see all submerged objects with the greatest of ease when the water is itself clear. The principle of the water-telescope is as simple as its construction; for the tube, protecting the surface of the water within it from the disturbances outside, prevents the light from being refracted successively in different directions, while the dead-black surface of the interior prevents those internal reflections that would otherwise cause the vision to be indistinct.

A few hours spent with the rhodosperms at the sea-side will be sufficient to show not only the great variety of their form and colouring, but also that the same species may vary according to the position in which it grows. Most of the smaller forms are delicate and filamentous, but others have expanded fronds which are very leaf-like. The brightest colours are usually to be found at or beyond low-water mark, where the weeds are covered with a considerable height of water for hours together, and also in shady situations at higher levels, while some of the species that grow in the upper rock pools are often of such a deep colour, with so much admixture of brown, that they may be easily mistaken for the olive melanospores to be presently described.

Most of the rhodosperms are attached directly to the rocks, and the larger species have often a root-like disc by which they are very firmly held; but some of the smaller species grow attached to larger weeds, into the substance of which they frequently penetrate; and it is possible that these derive some amount of nourishment from the sap of their supporters. Some are of a recumbent nature, being attached to the rock throughout their whole length, while others are so incrusted with carbonate of lime which has been extracted from the water that they resemble corals rather than forms of vegetable life. Nearly all of them contain a bright-red colouring matter in addition to the chlorophyll by which they are enabled to feed on carbonic acid gas.

None of the rhodosperms are of really microscopic dimensions, and they all grow by the repeated division of the cells of the apex, while the branches are derived by the similar division of new cells at the sides.

All plants are particularly interesting during the period of fruiting, and this is remarkably the case with many of our red-spored sea weeds, which are brighter and prettier while laden with their spore-producing cells; and the collector of marine algÆ should always endeavour to obtain as many species as possible in fruit, not only on account of the brighter appearance that may characterise them at this time, but mainly because the opportunity of studying the mode of reproduction should not be missed.

In the rhodosperms the reproduction may be either asexual or sexual. In the former case fertile spores are produced without the necessity for any outside fertilising element, and four are usually produced in each one of the sporangia, hence they are generally known as tetraspores. Where the reproduction is of the sexual type, the male cells are produced singly in the terminal cells of the fronds, and since they are usually crowded together in considerable numbers, and contain none of the red colouring matter that exists in the other parts of the plant, their presence is easily observed.

The female cells (carpogonia) are also produced on the tips of the branches, and when the male elements escape from their cells, they are conveyed passively by the movements of the water, for they have no vibratile cilia by which they are propelled, and on coming into contact with the female cell they adhere closely. An opening is then formed in the latter, and the male element enters the carpogonium, which germinates, deriving its nourishment from the parent plant, and the spores are thus formed. Lastly, it is interesting to note that the asexual spores, the male cells, and the female cells are generally produced on different plants of the same species.

We will now proceed to examine some of the best known and most interesting of the rhodosperms, beginning with the order CeramiaceÆ, which contains a number of red or reddish-brown weeds with jointed, thread-like fronds that enclose a single tube, and which are generally surrounded by a cuticle of polygonal cells. The spores are contained in transparent berry-like sacs which are naked; and the four-parted spores (tetraspores) are formed in the cells of the cuticle or at the tips of the fronds.

Over twenty British species belong to the genus Callithamnion, and nearly all of them are pretty red or rose-coloured, feathery plants that are conspicuous for their beauty. Nearly all are of small size, the largest measuring only seven or eight inches, while some are so small that they would scarcely be noticed except by those who search diligently for them. The principal features of the genus are, in addition to those mentioned above as common to the order, that the spores are angular, and clustered within a transparent sac, and the tetraspores are naked and distributed on the branches.

In some species the fronds have no stem, and these are very small, generally only about a quarter of an inch in height or less, and they grow on rocks or weeds, sometimes clothing the surfaces with a velvet-like covering. C. floridulum forms a kind of reddish down on the rocks, sometimes in little rounded patches, but sometimes completely covering the surface. It occurs on several parts of the English coast, but is so abundant on the west coast of Ireland that the beach is strewn with it after stormy weather. Other allied species grow in minute tufts on rocks, or are parasitic on other weeds, and are so inconspicuous that they are but little known.

Another section of the genus is characterised by pinnate fronds with opposite segments, and the species are very pretty plants with fronds generally a few inches in length. One of the commonest of these is the Feathered Callithamnion (C. plumula), a great favourite with collectors of sea weeds, and a most interesting object for the microscope. Its soft and flexible fronds grow in tufts from two to five inches long. The branches are regularly arranged, and the comb-like branchlets bear the tetraspores on the tips of the plumules. This beautiful weed grows near low-water mark, and in deep water, and is often very abundant on the beach after storms. C. Turneri is another common species, easily known by its creeping fibres, attached by little discs to some larger weed, and from which the tufts of branched fronds stand out erect. On the west and south-west coasts of Britain we may often meet with the allied Crossed Callithamnion (C. cruciatum), which grows on rocks, close to low-water mark, that are covered with a muddy deposit. It grows in tufts, somewhat resembling those of C. plumula, but its plumules are arranged two, three, or four at a level, and are very crowded at the tips of the branches.

Fig. 245.—Callithamnion roseum

Fig. 246.—Callithamnion tetricum

Still another section of this large genus contains weeds of a more shrubby growth, with veined stem and branches jointed obscurely. Of these the Rosy Callithamnion (C. roseum) is not uncommonly found on muddy shores, and especially in and near the estuaries of rivers. It grows in dense dark-coloured tufts, two or three inches long, with alternate branches much divided. The tetraspores occur singly, one at the top of each of the lower joints of the pinnules of the plumes. C. byssoideum grows on larger weeds in the rock pools, and especially on Codium tomentosum (p. 353), in dense tufts of exceedingly fine filaments, jointed, and branched irregularly. The upper branches are plumed, and their tips bear very fine colourless filaments. The spore-clusters are arranged in pairs, and the tetraspores are thinly scattered on the pinnules of the plumes. This species is so very delicate in structure that a lens is absolutely necessary to make out its structure. It is, in fact, impossible to distinguish between the various species of Callithamnion without such aid; and many of them, particularly the species last described, require the low power of a compound microscope.

Among the other common species, belonging to the same section, we may mention C. corymbosum, distinguished by its very slender, rosy, jointed fronds, with the ultimate divisions of the branches disposed in a level-topped (corymbose) manner, growing on rocks and weeds near low-water mark; C. polyspermum, growing in globular tufts on Fucus serratus and F. vesiculosus, with short awl-shaped pinnules, and closely-packed clusters of spores; C. Hookeri, with opaque stem and branches, and spreading branchlets that are themselves branched, and bear spreading plumules at their tips; and C. arbuscula, found on the west coasts, with a stout stem, naked below, and having a very bushy habit.

It is often by no means an easy matter to distinguish between the different species in such a large genus as Callithamnion, and we strongly recommend the beginner to first study the characteristics on which the classification of the AlgÆ is based, and to arrange his specimens according to the orders and genera to which they belong; and then, after mastering the principles of classification, he should refer to one of those larger works in which all known British species are described, and make himself acquainted with the features of each individual species in his collection.

Before leaving the present genus we ought also to mention the fact that many of the species lose their natural colour rapidly when placed in fresh water; hence when they are being cleansed for mounting salt water should be employed. Further, even after they have been satisfactorily mounted, they are liable to be spoiled if left exposed to moist air. The salt water used need not be the natural sea water; a solution of common table salt, made up to approximately the same strength as sea water, will answer the purpose just as well.

The genus Griffithsia includes some very beautiful weeds of delicate threadlike structure and of a fine rose colour. The frond contains a single tube, and is jointed and forked, the joints being usually transparent. The spore clusters are enclosed in a gelatinous sac surrounded by a whorl of little branchlets, the spores themselves being minute and angular. The tetraspores are attached to the inner side of whorled branchlets.

The commonest species is G. setacea, which is of a bright-red colour and slightly branched. It is also of a somewhat firm structure, but soon loses both firmness and colour when removed from salt water; and, like Callithamnion, rapidly fades if put into fresh water, which is readily absorbed through its membranes, causing them to burst and discharge their colouring matter. It receives its specific name from its bristle-like forked fronds. G. secundiflora is somewhat like Setacea, but is larger, and the tips of its branches are obtuse. Its fronds grow in fan-shaped tufts five or six inches long. It is not a common weed, but may often be met with on the coast of Devon and Cornwall.

Fig. 247.—Griffithsia corallina

G. barbata, or the Bearded Griffithsia, receives its name from its very delicate fibres, which bear spherical, pink tetraspores. It seems to occur only on the south and south-west coasts, where it grows on stones or attached to other weeds. Our last example of the genus is G. corallina, which is of a deep-crimson colour, and is so jointed as to have the appearance of a coralline. Its fronds are from three to eight inches long, regularly forked, and of a gelatinous nature. The joints are somewhat pear-shaped, and the spore clusters are attached to their upper ends. It soon fades, and even if its colour is satisfactorily preserved, the pressure of the drying press destroys the beautiful rounded form of its bead-like joints. It forms a lovely permanent specimen, however, when preserved in a bottle of salt water, with the addition of a single grain of corrosive sublimate.

Fig. 248.—Halurus equisetifolius

Fig. 249.—Pilota plumosa

Our next genus (Halurus) contains a common weed of the south coast which was once included in Griffithsia. It is the Equisetum-leaved Halurus (H. equisetifolius), so called because its branches are regularly whorled round the nodes of the jointed branches, thus resembling the semi-aquatic Mare’s Tail. Its frond is tubular, and the spore-clusters are situated on the tips of the branches, surrounded by a whorl of small branchlets.

The genus Pilota has a slightly flattened cartilaginous frond, divided pinnately, and the axis surrounded by a cuticle of two layers of cells. The spore-clusters, at the tips of the branches, are surrounded by a whorl of branchlets. It contains only two British species, one of which (P. plumosa) is a very feathery species, with comb-like branchlets, growing on the stems and fronds of other weeds found on our northern shores. The other (P. elegans), with narrower fronds, in long flaccid tufts, is found all round our coasts.

Our last genus of the CeramiaceÆ is the large and typical one Ceramium, which contains about a dozen British species in which the frond is threadlike, jointed, branched or forked repeatedly, with the tips of the branchlets usually curled. The spore-clusters are enclosed in transparent sessile sacs, surrounded by a whorl of very short branchlets; and the tetraspores are embedded in the cortex, but distinctly visible. As a rule the fronds are very symmetrical, and the branches radiate in a regular fan-like manner.

In one species of the genus the frond is completely covered with cortex cells, and at each node of the frond there is a single spine which, although so small as to be invisible without a lens, so effectually locks the threads together that they form an entangled mass that is not easily arranged to the satisfaction of the collector. The species referred to is C. flabelligerum—the Fan-bearing Ceramium—and is very rare except in the Channel Islands.

Other species are armed with one or more spines at the nodes, but the nodes only are covered with cortex cells, which render them opaque, while the internodes or joints are transparent. In this group we have C. ciliatum—the Hairy Ceramium, with reddish-purple segments, and a regular whorl of hairs, directed upwards, round each node; each hair or spine consists of three segments. This plant is common during the summer and autumn, and may be found in the tide pools at all levels, either attached to the rocks or parasitic on other weeds. The same section contains C. echinotum, with rigid, forked fronds, and irregularly-scattered one-jointed spines; it is common on the south coast, where it may be found on the rocks and weeds of the upper tide pools; and C. acanthonotum, also common in the rock pools, with a single strong three-jointed spine on the outer side of each filament. The last-named weed is found principally on the northern shores, especially on rocks covered with the fry of the common mussel.

Other species are characterised by transparent internodes as above described, but have no spines at the joints, and may thus be easily floated on to a sheet of paper without the troublesome matting of their fronds. These include the Straight Ceramium (C. strictum), with erect and straight branches growing in dense tufts, and conspicuous tetraspores arranged round the nodes of the upper branchlets, C. gracillimum, of the lower rock pools, with very slender gelatinous fronds, swollen nodes and small fan-shaped branchlets; C. tenuissimum, closely resembling C. strictum in general appearance, but distinguished by having its tetraspores only on the outer side of the nodes; and the Transparent Ceramium (C. diaphanum), which may be found throughout the year on rocks and weeds in the rock pools. The last species is the largest and most beautiful of the genus, and may be readily recognised by its light-coloured, transparent stem with swollen purple nodes, and its conspicuous spore-clusters near the tips of the filaments.

Fig. 250.—Ceramium diaphanum

Our last example of the genus is the Common Red Ceramium (C. rubrum), which may be found in the rock pools at all levels. It is very variable in form, but may be known by its contracted nodes, in which the red tetraspores are lodged, and its spore-clusters surrounded by three or four short branchlets. It differs from most of the other species in having both nodes and internodes covered with cortex-cells, and hence the latter are not transparent.

The order SpyridiaceÆ has a single British representative which may be found in various localities on the south coast. It is Spyridia filamentosa, a dull-red weed with thread-like, tubular, jointed fronds, from four inches to a foot in length. The main stem is forked, and densely clothed with short and slender branchlets. The frond is covered with a cortex of small cells. The spore-clusters are grouped together, several being enclosed in a membranous cell in conceptacles, or external sacs, at the ends of the branchlets; and the tetraspores are arranged singly along the jointed branchlets.

The next family (CryptonemiaceÆ) is an extensive one, containing nearly twenty British genera of red or purple weeds, with unjointed, cartilaginous, gelatinous, and sometimes membranous fronds. The spores are irregularly distributed, and are contained either in sunken cells or in conceptacles. The tetraspores are either in cells at the edges of the frond or collected together in compact groups.

Of the genus Dumontia we have only one species (D. filiformis), the frond of which is a simple or branched tube, from an inch to more than a foot in length, containing a loose network of filaments when young, and only a gelatinous fluid when the plant is mature. The spores exist in rounded clusters among the cells of the tube, and the tetraspores are similarly situated. A variety with wide wavy fronds is sometimes found in the brackish water near the mouths of rivers.

Gloiosiphonia capillaris is a very delicate and beautiful weed found in the lowest tide pools of the south coast. Its frond is a very slender branched tube, filled with a gelatinous fluid, and composed of delicate filaments embedded in transparent gelatine. It is a beautiful object for the microscope.

Schizymenia (IridÆa) edulis has flat, oval, dark-red fronds that grow in clusters; and, being eaten by various marine animals, is often found imperfect and full of holes. The fronds are sometimes a foot or more in length, and five or six inches wide. They are thick and leathery, and each is supported on a short, cylindrical stem.

In the lower tide pools we commonly meet with Furcellaria fastigiata, with brownish-red, cylindrical fronds, solid, forked, and densely tufted. The branches are all of the same height, with sharp tips; and the spore-clusters are contained in terminal lanceolate pods. This weed is very much like Polyides, of another order, but may be distinguished by its fibrous, creeping root, while that of Polyides is a disc.

The genus Chylocladia is characterised by a tubular rounded frond composed of two layers, the inner consisting of branching filaments, and the outer cellular. The spores are contained in external cones with a pore at the apex, and the tetraspores are among the superficial cells of the branches. There are two common British species of the genus, one of them—C. articulata—with long, tubular fronds, constricted at intervals, the lower branches forked and the upper whorled and tufted; and C. clavellosa, with freely branched fronds bearing short spindle-shaped branchlets.

One of the best-known algÆ of the present family is the Irish Moss or Carrageen (Chondrus crispus), which will be at once recognised by its representation on Plate VIII. Its fronds are cartilaginous, forked and fan-shaped; and, when growing in deep, sheltered pools, its branches are often broad and much curled. This weed is an important article of commerce, being still used as a food for invalids. When boiled it yields a colourless gelatine.

In the genus Gigartina the frond is cartilaginous, flat, or threadlike, irregularly branched, and of a purplish-red colour. The spores are contained in external tubercles, and the tetraspores are arranged in masses beneath the surface. The only common species is G. mamillosa, which has a linear, furrowed stem, with fan-shaped, deeply-cleft fronds. The spores are contained in mamilliform tubercles scattered over the surface of the frond.

Callophyllis (Rhodymenia) laciniata is found on most rocky coasts. It has bright-red, fleshy fronds that are deeply cleft into wedge-shaped segments, the fertile specimens with waved edges and small marginal leaflets. It is found on rocks and Laminaria stems beyond the tide-marks, but is commonly washed up on the beach during storms. It is a beautiful weed, and retains its colour well when dried.

Cystoclonium (HypnÆa) purpurascens is a very common weed, growing on other algÆ between the tide-marks, and sometimes reaching a length of two feet. Its cartilaginous, purple fronds are much branched, and become almost black when dried. The spores are embedded in the smallest branches, and the tetraspores are arranged among the superficial cells.

The genus Phyllophora contains a few British weeds with a stiff, membranous frond, bearing leaf-like appendages, and supported on a stalk. The tetraspores are contained in external wart-like swellings. The commonest species is P. membranifolia, the fronds of which are divided into wedge-shaped segments, and grow in tufts from an expanding root. The spores are contained in stalked sporangia, and the tetraspores are near the centres of the segments. Another species—P. rubens—has a shorter stem, and grows in deep and shady rock pools. Its fronds are densely tufted; and, as the plant grows, new series of segments are formed at the tips of the older ones. A third species (P. palmettoides) has a very bright-red frond and an expanded root.

The order RhodymeniaceÆ includes a number of red or purple sea weeds with flat or thread-like unjointed, cellular fronds, the surface cells forming a continuous coating. The spores are lodged in external conceptacles, and are at first arranged in beaded threads. The tetraspores are either distributed among the surface cells, collected in clusters, or situated in special leaflets.

The typical genus (Rhodymenia) contains two red, membranous weeds, the commoner of which is R. palmata (Plate VIII.), so common on the Scottish and Irish coasts, where it forms an important article of diet, and is known as the Dulse or Dillisk. It is also widely distributed over the English coasts. Its broad, fleshy fronds are divided into finger-like lobes, and are either sessile or supported on a stalk that proceeds from a small discoid root. The frond is very variable in form, being sometimes divided into very narrow segments, and sometimes quite undivided. One variety has a number of small stalked leaflets on its margin (see Plate VIII.); and another is very narrow, with wedge-shaped irregular lobes. R. palmetta is a smaller and less common species that grows on rocks and large weeds in deep water. The tetraspores form crimson patches on the tips of the lobes.

Maugeria (Delesseria) sanguinea (Plate VIII.) is a large and beautiful weed, of a blood-red colour, that grows in the lower rock pools or beyond low-water mark, under the shade of high rocks or hidden by the olive tangles. Its frond is thin and membranous, with a well-defined midrib. The spores are contained in globular stalked conceptacles, usually on one side of the midrib; and the tetraspores may be seen in pod-like leaflets attached to the bare midrib during the winter.

Passing over some of the rarer membranaceous RhodymeniaceÆ, we come to the beautiful Plocamium, distinguished by its linear compressed crimson fronds, which are pinnate, with comb-like teeth, the branchlets being alternately arranged on either side in threes and fours. The spores are on radiating threads, in globular conceptacles; and the tetraspores are in the outer divisions of the frond. We have only one species of this beautiful genus, and that is P. coccineum, which is of such a brilliant colour that it is always a favourite with collectors.

Fig 251..—Plocamium

Our last example of the order is Cordylecladia (Gracilaria) erecta, with threadlike, cartilaginous frond, irregularly branched and cellular in structure. The fronds arise from a disc-like root; and bear spores in thickly-clustered spherical conceptacles, and tetraspores in lanceolate pods at the tips of the branches, both in the winter. It is a small weed, and grows principally on sand-covered rocks near low-water mark.

The order SphÆrococcoideÆ contains red or purple sea weeds with unjointed cartilaginous or membranaceous fronds, composed of many-sided, elongated cells, with spores in necklace-like strings, lodged in external conceptacles. The typical genus (SphÆrococcus) contains the Buck’s-horn sea weed which grows at and beyond low-water mark on the south and west coasts, where it is sometimes washed up on the beach during storms. Its fronds are flattened and two-edged, freely branched, and the upper branches are repeatedly forked, and terminate in fan-shaped, cleft branchlets. Both branches and branchlets are fringed with slender cilia, in which the spores are embedded. It is a handsome weed, of a bright-red colour and a somewhat coral-like form.

Allied to this is Gelidium corneum, with flattened, horny fronds, repeatedly pinnate, with the smallest branchlets obtuse and narrower at the base. The spores are contained in conceptacles near the extremities of the branchlets, and the tetraspores are imbedded in club-shaped branchlets. There are a large number of varieties of this species, differing in form, size, and the mode of branching of the fronds. The size varies from one to five or six inches, and the colour is red or reddish green.

In the genus Gracilaria the frond is thick and horny, and the surface cells are very small, while the central ones are large. The spores, formed on necklace-like threads, are enclosed in sessile conceptacles along the branches, and the tetraspores are imbedded among the surface cells of the fronds. The only common species is G. confervoides, with cylindrical cartilaginous fronds bearing long thread-like branches, sometimes reaching a length of two feet. The spore conceptacles are situated on the slender branches, giving them a knotted or beaded appearance. The colour is a dark purple, which rapidly fades when the weed is placed in fresh water or left exposed to the air. Two other species—G. multipartita and G. compressa—are rare.

Calliblepharis ciliata, perhaps more commonly known as Rhodymenia ciliata, has a branching root, short round stem, and a broad, crisp frond that is generally ciliated. Sometimes the frond is simple and lanceolate, with small leaf-like appendages on its edge; and sometimes it is deeply cleft. The spores are arranged in beaded threads in sessile conceptacles on the marginal leaflets. Another species of the same genus (C. jubata) is very similar in structure, but is of a duller-red colour, gradually changing to olive green at the tips; and it has its tetraspores in the cilia only, while in C. ciliata they are collected in patches in all parts of the frond. Both species grow in deep water, and are frequently washed up during storms.

The large genus Nitophyllum contains some beautiful rose-red sea weeds, with irregularly cleft membranaceous fronds, either veinless, or with a few indistinctly visible veins only at the base. The spores are in rounded sessile conceptacles scattered on the surface of the frond; and the tetraspores occur in clusters similarly scattered.

One of the species—N. laceratum—so called from the torn and jagged appearance of the frond, is represented on Plate VII. The fronds are attached to a disc-like root, and are very variable in form, being sometimes so narrow as to appear almost threadlike. The plant grows on rocks and large weeds in the lower rock pools and in deep water. In the same genus we have N. punctatum, with broad pink fronds, dotted all over with spore-conceptacles and dark-red clusters of tetraspores; also a few other less common species that are seldom seen except after storms, as they grow almost exclusively in deep water.

The genus Delesseria contains some beautiful rose-coloured and reddish-brown weeds with delicate, leaf-like, symmetrical fronds, each of which has a darker midrib from which issue transverse veins. The spores are arranged like minute necklaces, and are contained in sessile conceptacles either on the midrib of the frond or on leaflets that grow from the midrib. The tetraspores are in clusters which are scattered over the frond or on its leaflets. The algÆ of this genus are seldom found growing between the tide-marks, as they generally thrive in deep water, but splendid specimens are often washed up on the beach during storms, especially on the south and south-west coasts.

Among these we may specially mention D. alata, known popularly as the Winged Delesseria, with a dark-red, forked frond, consisting of a strong midrib, bordered by a wing-like lamina of very variable width, supported by opposite veins. In this species the clusters of tetraspores are arranged on each side of the midrib or special leaflets near the tips of the frond. D. sinuosa is a less common weed, with a disc-like root and an oblong, cleft and toothed frond, and tetraspores in leaflets growing from its margin. Another species—D. hypoglossum—is characterised by the leaflets of the midrib bearing still smaller leaflets in the same manner.

We have already referred (p. 366) to a sea weed commonly known as the Dock-leaved Delesseria, the scientific name of which is Maugeria (Delesseria) sanguinea. This plant was once included in the present order, but has been removed on account of the different structure of its fruit.

Our next order is the interesting one containing the coral-like weeds, some of which are so common and so conspicuous in the rock pools. The order is known as the CorallinaceÆ, and all its species secrete carbonate of lime, which hides their vegetable structure and gives them more the appearance of stony corals.

The typical genus (Corallina) includes two weeds with jointed pinnate fronds, and spore-conceptacles at the tips of the branches with a terminal pore.

These and the allied sea weeds are very unlike plants in their general nature, their stony covering of carbonate of lime hiding all traces of the delicate cellular structure so characteristic of the various forms of vegetable life, and especially those of aquatic or marine habit. If, however, the weed is put into dilute hydrochloric (muriatic) acid the calcareous matter will be completely dissolved in a minute or two, with evolution of bubbles of carbonic acid gas; and if a portion of the frond be then examined in a drop of water under the microscope, the cellular structure referred to will be seen as well as in any other weed. Another characteristic of the plant, or rather of the carbonate of lime which it secretes, is its property of becoming intensely luminous when held in a very hot flame. Thus if a tuft of coralline be held in the flame of a Bunsen burner, it will glow so brilliantly as to remind us of the lime light. Further, if we examine the plant in its natural state, we find that the carbonate of lime is not secreted uniformly in all parts, but that the nodes of the jointed frond are free from the stony deposit, and are therefore flexible.

Our commonest species—C. officinalis—may be found in almost every rock pool between the tide-marks, growing on rocks, shells, and other weeds. The joints of the stem and branches are cylindrical or somewhat wedge-shaped, while those of the branchlets are linear; and the colour varies from a dark purple to white, the former prevailing in the deep and shady pools and the depth of tint decreasing according to the amount of exposure to the bleaching action of the sun.

A second species (C. squamata) is very similar in growth and habit, but is much less common, and is confined to the neighbourhood of low-water mark. It may be distinguished from the last by the form of the segments, which are short and globose in the lower portions of the stem, and become broader and more flattened towards the tips of the branches.

Another genus—Jania—contains a few coralline weeds that are somewhat like Corallina, but are of a more slender habit and smaller, and have a moss-like appearance. They may be distinguished by the forked branching of the slender frond, and by the position of the conceptacles in the axils of the branches, and not at the tips. J. rubens is a very common red species that grows in tufts on other weeds. It has cylindrical segments, longer towards the tips of the branches; while another and less common one (J. corniculata), found principally on the south coasts, has flattened segments except in the branchlets.

A third genus of the order—Melobesia—contains a very peculiar group of algÆ that would certainly never be regarded as plants by those who did not know them. They are apparently mere solid incrustations of calcareous matter, without any jointed structure, and often of very irregular form, covering the surfaces of rocks, shells, or weeds. They are of varying colours, some prevailing tints being dark purple, lilac, rose, and yellow; and they are equally variable in form, some being decidedly lichen-like, some resembling fungoid masses, and others consisting of superimposed leaf-like layers. They are not weeds to be pressed for the collector’s album, but require storing in boxes or trays like sea shells. As in the case of the branched corallines, the hidden vegetable structure may be revealed by dissolving away the carbonate of lime; and the spore-conceptacles, with terminal pores, may be seen scattered irregularly over the surface.

The order LaurenciaceÆ contains some beautiful pink, red, and purple weeds with round or flattened branching fronds. They may be known by the disposition of the tetraspores, which are irregularly scattered over the branches; and by the pear-shaped spores in rounded capsules. The typical genus (Laurencia) includes an abundant weed (L. pinnatifida) which was formerly eaten in parts of Scotland, where it is known as the Pepper Dulse on account of its peppery taste. It is found in the tide pools on many parts of the coast, and varies much in size, form, and colour according to the situation in which it grows. The plants which are exposed to the air at low tide are usually small, and of a pale brown colour, while those found in the permanent rock pools at or near low-water mark are larger and dark brown or purple. The fronds are flat and cartilaginous, with stout branches bearing alternate divided branchlets, which are blunt at the tips. The stem itself is unbranched. The spores are pear-shaped, in oval cells; and the tetraspores are irregularly distributed near the tips of the branches.

Another common species, known as the Tufted Laurencia (L. cÆspitosa), is very similar to the last mentioned, and is not easily distinguished from it. It is, however, of a bushy habit, while L. pinnatifida is flat, and its fronds are less firm. This species grows on rocks and stones between the tide-marks, and is variegated in colour from a pale green to a purple.

A third species—the Obtuse Laurencia (L. obtusa)—is widely distributed on our coasts, and may be known by its thread-like bipinnate fronds with short blunt branchlets, cup-shaped at the tips. It is parasitic on various other weeds.

The genus Lomentaria includes a few weeds with tubular fronds that are constricted at intervals, and divided internally by transverse membranous septa. The spores are pear-shaped and lodged in spherical cells; and the tetraspores are scattered on the surface of the branches. One species called the salt-wort (L. kaliformis) is widely distributed. Its colour is pink, sometimes yellowish, and it grows on rocks or stones, and sometimes on other weeds. It may always be known by its spherical fruit, without any visible opening, containing crimson pear-shaped spores. Another species (L. ovalis), found on the coasts of Devon and Cornwall, may be recognised by its solid branched frond and little oval leaf-like branchlets, which are hollow, jointed, and divided by partitions internally.

The one remaining order of the red-spored sea weeds is the RhodomelaceÆ, which has either a jointed or a many-tubed axis, and the surface divided up into little definite areas. The fronds are either leafy or thread-like, and the prevailing colours are red, reddish brown, and purple. The spores are pear-shaped, and occupy the terminal cells of tufted threads in external, globular, or rounded conceptacles; and the tetraspores are lodged in special receptacles, or in special modified branchlets. The order contains some of our most beautiful weeds, while some of its members are of a very dark colour and unattractive form.

The typical genus—Rhodomela—contains two British species with dark-red, cartilaginous fronds, cylindrical, unjointed, and irregularly branched; and the tetraspores imbedded in the tips of the slender branchlets. The name of the genus signifies ‘red-black,’ and is applied on account of the tendency of the dark-red fronds to turn black when dried.

R. subfusca is very common on all our coasts. It has rigid fronds, irregularly branched; and is in its best condition during the summer. The other species—R. lycopodioides—has long undivided branches with thickly-set and freely-divided branchlets.

When turning over the fronds of different species of the larger olive weeds we commonly find them more or less clothed with tufts of filamentous plants, sometimes small and delicate, and sometimes larger and of more robust growth, varying in colour from a purplish brown to a dark violet, and the articulated filaments more or less distinctly striated with parallel lines. These weeds belong to the genus Polysiphonia, and derive their generic name from the fact that the threadlike fronds are composed of several parallel tubes. The surface cells are also arranged in regular transverse rows, and it is this which gives rise to the striated appearance above referred to.

Over twenty species of Polysiphonia are to be found on our shores, where they exist at all levels between the tide-marks. They are distinguished from one another partly by their general form and mode of growth, and also by the number of tubes in their threadlike fronds.

Although they would not always be considered as lovely weeds and are often anything but beautiful when dried and mounted, yet in their fresh condition they are generally pretty objects, and their microscopic structure is particularly interesting on account of the beautiful and symmetrical arrangement of their siphons and tubes.

If the reader is the fortunate possessor of a compound microscope, it will amply repay him to make transverse sections of the fronds for examination. A short length of the frond should be inserted into a slit cut in a piece of carrot or elder pith; and, while thus supported, very thin transverse sections may be easily cut with a sharp razor, care being taken to keep both razor and object very wet during the process. Allow the sections to fall into a vessel of water as they are cut, and then select the thinnest for examination, mounting them in a drop of water in the usual way.

Specimens in fruit should always be obtained when possible, so that the nature of the fructification may be observed. Two kinds of spores may be seen in each species, but, as is usually the case with the red sea weeds, on different plants. Some are small pear-shaped bodies, enclosed in oval cells at the tips of the fronds; and the others are arranged in clusters of four in swollen parts of the threads.

The commonest species is P. fastigiata, which may be found in abundance as bushy brownish tufts on the fronds of Fucus nodosus (p. 386). A transverse section of this weed is a very beautiful microscopic object. It resembles a wheel, with a dark centre to the nave, and several spokes enclosing about sixteen regularly arranged tubes. The swollen tips of fronds should also be examined for the urn-shaped cells containing the spores; and if a gentle pressure be applied to the cover-glass with a needle, the little pear-shaped spores may be expelled. The other kind of spores may be found near the bases of the branches on different plants.

Among other species we may briefly mention—P. parasitica, sometimes found near low-water mark, growing in little feathery tufts of a bright-red colour, on the lichen-like Melobesia or on corallines. It has seven or eight parallel siphons in its fronds, all regularly arranged round a small central space.P. BrodiÆi is moderately common on our coasts. This is a large brown species, with seven siphons surrounded by a thick cellular layer which conceals the articulations and is too opaque to allow the siphons to be seen without dissection. Its branches, which are alternate, bear short tufts of delicate branchlets.

P. byssoides, so called on account of the pink filaments that fringe the fronds, has also seven siphons. It is a large and beautiful weed, moderately common on our coasts, of a bright-red colour, with conspicuous fructification. The branches are alternate, and the branchlets are clothed with the byssoid filaments above referred to.

P. violacea is of a reddish-brown colour, with long silky alternate branches, and four siphons. It receives its specific name from the fact that it turns to a violet colour when dried.

P. nigrescens has, as the specific name implies, blackish fronds, and these are freely branched. The tubes, about twenty in number, are flat, and are arranged round a large central space.

Our last example—P. atro-rubescens—is of a dark reddish-brown colour, with rigid and densely-tufted fronds. It has twelve tubes, arranged spirally round a central cavity. It is common in the lower rock pools of some coasts.

In the same order we have the genus Chondria, so called on account of the cartilaginous nature of its thread-like fronds. These are pinnately branched, and the club-shaped branchlets taper below. The main stem is jointed and contains many siphons. The genus includes a common species (C. dasyphylla), with thick fronds, that is found in shallow sandy pools, where it grows on pebbles, shells, or on other weeds, the colour varying from pink to a dark purple. C. tenuissima is a very similar weed, but may be distinguished by its more slender growth, and by its long, rod-like simple branches, clothed with slender, bristle-like branchlets that taper from the middle towards both ends.

On the northern coasts of Britain we may meet with Odonthalia dentata, the blood-red fronds of which are tufted, and arise from a hard, disc-like root. Each frond projects from the axil of a tooth-like projection of the main stem, and is deeply pinnatifid, with a distinct midrib in the lower part, and thin and membranaceous towards the tip. The pinna are dentate, and the spores are in stalked, oval conceptacles in the axils of the pinnÆ. The tetraspores are similarly situated in stalked, lanceolate leaflets.

The weeds of the genus RytiphlÆa are very similar to some of the Polysiphonia, the axis of the frond being jointed and transversely striped, but the nodes are less distinct and are not constricted. They are shrub-like weeds, with tufted spores in oval, sessile conceptacles; and tetraspores in spindle-shaped branchlets or in little pod-like leaflets. The principal British species are:—

R. pinastroides, a much-branched and shrub-like weed, of a dull-red colour, which turns black when the plant is dried. The branches have rigid, hooked branchlets arranged in such a manner as to give a combed appearance. This species occurs on the south coast, and is in its prime in very early spring. It is often rendered peculiarly interesting by the colonies of zoophytes and the patches of Melobesia with which it is more or less covered.

R. fruticulosa is another shrubby species, with irregularly branched, interlacing stems. It is to be found in the rock pools of the south and west coasts, and is of a deep-purple colour in the deeper shady pools, but varying to a yellowish tint where exposed to the full light of the sun. The whole of the frond is covered with hooked branchlets, and the weed is peculiar for the fact that, when removed from the rock pool, little glistening beads of water remain attached to the tips of the terminal branches. The tetraspores are situated in distorted branchlets.

R. thuyoides has creeping, fibrous roots, from which arise the erect stems of purple-brown, branched fronds with short spine-like branchlets. It occurs in the shallower rock pools, where it grows attached to rocks or to other weeds. It is in its best condition during the summer, when we may see its oval spore-conceptacles and the tetraspores in distorted branchlets.

The last genus of the RhodomelaceÆ is Dasya, which contains some very graceful and brightly-coloured weeds that are found principally on our south and west coasts. In these the fronds are thread-like or flattened, branched, and without visible joints. The main stem contains many tubes, but the tubular structure is hidden by the outer layer of cells; and the branchlets, which are slender, one-tubed, and jointed, bear little lanceolate pods that contain the tetraspores.

D. ocellata has small tufted fronds, about two or three inches long, attached to a small discoid root. The main stems are densely covered with slender, forked branchlets, those at the tips being clustered in such a manner as to recall the eye-like marks of the peacock’s tail. It grows principally on the mud-covered rocks beyond low-water mark, and is not by any means a common weed. Another species—D. arbuscula—is somewhat plentiful on parts of the Scottish and Irish coasts, but comparatively rare in South Britain. It has a small disc-like root, and stems thickly clothed with short branchlets. The spore-conceptacles are tapering, on short stalks, and the tetraspores are contained in pointed pods on the branchlets. The scarlet Dasya (D. coccinea) may be commonly seen at and beyond low-water mark during late summer, at which time splendid specimens may also be found on the beach after storms. Its stem is thick, proceeding from a discoid root, and is clothed with hair-like filaments; and the branches bear short, slender branchlets that give them a feathery appearance. The tetraspores are contained in elongated, pointed, and stalked pods. There are three other species on the British list, but they are not common weeds.

The last of the three great groups into which the sea weeds are divided is the MelanospermeÆ, or olive-spored algÆ, the different species of which are generally very readily distinguished by their olive-green or olive-brown colour, for the whole plant, as well as the spores, contains a dark olive colouring matter, in addition to the chlorophyll which is always present.

These weeds are often very large, frequently attaining a length of twenty feet or more in our seas, and from eighty to a hundred feet in warmer parts; and, being also extremely abundant almost everywhere, they form a most conspicuous feature of the shore. They usually grow on rocks and stones, from high-water mark to moderately deep water, but some of the smaller species are pseudo-parasitic on other algÆ.

Their form is most varied. Some are minute filamentous plants, consisting only of slender jointed threads, and others are mere shapeless masses; but many of the larger species exhibit a great differentiation of form, having root-like and stem-like structures, and expansions that resemble leaves. The latter, too, often have large vesicles that contain air, sometimes arranged singly along the median line of the frond, or in lateral pairs, or a single vesicle at the base of each segment of the thallus.

The air vesicles, of course, serve to buoy up the plant when it is submerged, thus enabling the light to penetrate between its fronds to lower portions; and when the plants have been wrenched from their moorings by the force of the waves, they immediately rise to the surface and are drifted on to the shore or accumulate in the eddies of the surface currents. In this way immense masses of floating weeds are formed, the most remarkable being that of the Sargasso Sea in the North Atlantic.

Like other algÆ, the melanospores grow by a continued process of cell-division, and when portions of the thallus are worn away during stormy weather, they are renewed by the same process.

The cell-walls of many species are very mucilaginous, the gelatinous covering being either the result of the degeneration of the cell-walls themselves, or the secretion of special glands.

As with the last division, the reproduction of the melanospores may be asexual or sexual. The asexual spores, which are not motile, are formed in some of the surface cells of the thallus. The male and female sexual organs, called respectively the antheridia and the oogonia, are produced in cavities on special portions of the thallus, both kinds being often formed in the same cavity or depression. The latter contains from one to eight little bodies called oospheres. These escape and float passively away when the wall of the oogonia ruptures. The antheridia are also discharged whole, but the minute fertilising elements (antherozoids), which are eventually set free from them, swarm round the oospheres, being attracted by the latter. Soon one of the antherozoids enters the oosphere, and from that moment all attraction ceases, the remainder of the antherozoids floating passively away; and the oosphere, previously naked and barren, now develops a cell-wall, and becomes the fertile progenitor of a new plant.Starting with the lowest of the melanospores, we first deal with the order EctocarpaceÆ, which is characterised by olive, thread-like, jointed fronds, with spores on the branchlets or embedded in their substance; two kinds of spores often existing in the same plant.

The typical genus (Ectocarpus) contains many British species, though several of them are rare. They are soft and flexible weeds, generally of a dull olive colour, with slimy, tubular fronds, and grow in tufts on other weeds or on mud-covered rocks. Spores of various shapes are scattered over the fronds, and are also contained in pod-like bodies formed of the branchlets. This latter feature is, perhaps, the best distinguishing characteristic of the genus, but it is not an easy matter to identify the several species it contains.

E. tomentosus is very commonly found on Fucus and other weeds, where it forms matted tufts of slender threads of a yellowish-brown colour. The threads are clothed with transparent cilia, and together form a dense, spongy mass. The spores are contained in narrow pods supported on short stalks. E. littoralis is another common species, of a very unattractive appearance. It grows in matted tufts on other weeds, on rocks, mud, or any submerged object, and its spores are contained in linear swellings of the branches. This species thrives well in brackish water, and may be seen far up certain tidal rivers.

Among the other species we may briefly mention E. granulosus, an abundant and beautiful weed that grows in feathery tufts on rocks and weeds, with elliptical, stalkless pods, quite visible to the naked eye, freely distributed over the opposite branchlets; E. siliculosus, a pale olive, parasitic species with lanceolate stalked pods, pointed and striped; E. sphÆrophorus, a small, soft, brownish-yellow species, with dense matted branches and spherical pods arranged either opposite to one another or to a branchlet; and E. Mertensii, a pretty species that grows on muddy rocks, freely branched but not matted, and having pods enclosed by the branchlets. The last species is rare, but may be found in Cawsand Bay and a few other localities about Plymouth Sound. The genus includes several other species, but all these are more or less rare.

In the genus Myriotrichia we have two parasitic species with fragile, hair-like, jointed fronds bearing simple straight branches that are covered with transparent fibres. In these the spore-cases are rounded and transparent, and arranged along the main threads; and the dark olive spores are readily visible within. In M. filiformis the branchlets are short, and clustered at intervals, thus giving a somewhat knotted appearance to the threads, and both branches and branchlets are covered with long fibres. The other species—M. clavÆformis—is very similar, but may be distinguished by the arrangement of the branchlets, which are not clustered at intervals, but are distributed regularly, and are longer towards the tip of the frond, giving the appearance of minute fox-brushes.

The genus Sphacelaria contains several British weeds with rigid branched and jointed fronds, most easily distinguished by the tips of the branches, which are flattened, contain a granular mass, and have a withered appearance. S. cirrhosa forms hair-like tufts of slender fibres with closely-set branches on small weeds, the tufts varying from a quarter of an inch to over an inch in length. The fronds are naked at the base, and the spore-cases, which are globular, are arranged on the branches. S. filicina is, as its name implies, of a fern-like appearance, but is very variable in form. Its fronds vary from one to three inches in length, and the spores are arranged singly in the axils of the branchlets. Excluding some rarer species we mention one other example—the broom-like S. scoparia, the frond of which is coarse and very rigid, of a dark-brown colour, two or three inches long, with the lower portion clothed by woolly fibres. Its spores are arranged in clusters in the axils of the branchlets.

The last genus of the EctocarpaceÆ is Cladostephus, which grows in dark-green tufts, usually five or six inches long, in the deeper tide pools. The fronds are cylindrical, branched, inarticulate, and rigid; and the branchlets, which are short and jointed, are arranged in whorls. The spores are situated in short accessory branchlets, or in masses at the tips of the ordinary branchlets. C. verticillatus is a very common species, the whorled branchlets of which are deciduous in winter, when the accessory branchlets that bear spores begin to develop. C. spongiosus is densely clothed with branchlets, and is of a bushy habit, with a very spongy feeling. It is by some regarded as a variety of C. verticillatus.

The order ChordariaceÆ is characterised by a compound gelatinous or cartilaginous frond, consisting of interlacing horizontal and vertical threads. The spores are not external as in the EctocarpaceÆ, but contained in cells in the substance of the frond. In the typical genus the frond has a cylindrical, branched, cartilaginous axis, surrounded by whorls of club-shaped threads and slender gelatinous fibres. We have only one common species—Chordaria flagelliformis, the fronds of which are from four to twenty inches long, of uniform thickness throughout, with long, glistening, soft and slimy branches among which the spores are disposed. It may be found in rock pools at almost all levels.

In the genus Elachista there are some very small and peculiar weeds that are almost sure to be overlooked by inexperienced collectors. They are parasitic, and are composed of two kinds of jointed threads, the inner of which are forked and combined into a tubercle, while the outer are simple and radiate from the tubercle. The spores are attached to the inner threads. The largest species (E. fucicola) is parasitic on Fucus, growing in brush-like tufts about an inch long. Some of the smaller ones are mere star-like tufts of no attractive appearance, and would be disregarded as troublesome parasites by most young collectors, but all of them are very interesting objects for the microscope.

The members of the genus Myrionema are similarly liable to be neglected, for they are minute parasites appearing only as decaying spots on larger weeds, but nevertheless form interesting studies for the microscope. Like the last group, they have two sets of jointed fibres, the inner being branched, and spread over the surface of the plant on which it grows, while the outer are simple and stand out at right angles, but all are united into a rounded mass by a gelatinous substance. Perhaps the best known is M. strangulans, which infests Ulva and Enteromorpha, producing the appearance of small decaying spots.

In the genus Leathesia we have other unattractive weeds, the jointed and forked threads of which are all united together into tuber-like fronds that are common on rocks and weeds between the tide-marks. There are three or four species, all similar in general appearance, with the spores distributed among the outer threads. These weeds cannot be satisfactorily pressed and dried in the usual way, and should be preserved in formaldehyde or dilute spirit, when they will always be available for microscopic examination.

The last genus of the ChordariaceÆ is Mesogloia, so called because the central axis of loosely-packed, interlacing threads is covered with gelatinous substance. Around this axis there are radiating, forked threads which are tipped with clubbed and beaded fibres among which the spores are distributed. One species (M. vermicularis), common in most rock pools, is of a wormlike form, of a dirty olive or yellow colour, with soft, elastic fronds growing in tufts from one to two feet long. M. virescens, also a common species, is of a pale greenish or olive colour, and very soft and slimy. Its stem is round and slender, freely branched, with short, simple branchlets.

The order DictyotaceÆ contains the olive weeds with inarticulate fronds, and superficial spores disposed in definite lines or spots. In the typical genus (Dictyota) the frond is flat and forked, somewhat ulva-like and ribless, and the spores are produced in little superficial discs just beneath the cuticle. There is only one British species—D. dichotoma—but that is a very common one, and it assumes a great variety of forms as regards the shape and division of its fronds according to the situation in which it grows, the fronds being broadest and strongest in the deepest water. The root is covered with woolly fibres, and the frond is regularly forked.

One of the most interesting algÆ of this order is the Turkey-feather Laver (Padina pavonia), which is the only British representative of its genus (see Plate VII.). Its very pretty fan-shaped fronds are of a leathery nature, curved, fringed along the upper margin, and marked with concentric lines. They often bear small leaflets, and are partially covered with a powdery substance which renders them beautifully iridescent when in the water. The root has woolly fibres, and the spores are arranged in lines along the upper margin. This weed seems to be confined to the south coast, where it may often be seen in the deeper tide pools; though in some of the sandy bays of the Isle of Wight it may be seen in shallow pools, and even in places left exposed to the air at low tide.

The genus Zonaria contains a British species (Z. parvula) that covers the rocks in round patches; and though moderately common is not very frequently seen by collectors on account of the fact that it grows in the deep crevices of rocks at or near low-water mark. Its frond is flat and membranaceous, more or less divided into lobes, without veins, and rather obscurely divided into concentric zones. It is attached to the rock by fibres that proceed from the under surface of the frond, and the spores are arranged in clusters beneath the superficial cells.

Cutleria multifida, though not very abundant, is to be found on most of our coasts; but since it grows almost exclusively beyond low-water mark, it should be looked for on the beach after storms, or in the fishermen’s nets. The frond is olive-green, fan-shaped, rather thick, and irregularly divided into forked branches; and it has a beautifully netted surface. The spore-cases may be seen scattered over the surface of the frond as so many black dots, and the antheridia are elongated, cylindrical bodies attached to tufted filaments on all parts of the frond.

In the genus Stilophora the root is discoid; the frond cylindrical, hollow, and branched; and the spores arranged in clusters over the surface. One species (S. rhizodes) is occasionally to be seen on the south coast. It is of a yellowish colour, from six to twenty inches long, and may be known by its long thread-like branches, with scattered, forked branchlets, and by the wart-like projections of the stem which contain the spores. This weed is often the source of some disappointment to the collector, for it soon turns to a jelly-like mass when removed from the water, and should therefore be mounted as soon as possible after it has been collected.

The fennel-like Dictyosiphon foeniculaceus is abundant in tide pools, where it may be seen in its best condition during spring and early summer. Its root is a small disc, the frond is tubular, thread-like and branched, and the branches bear hooked branchlets. The spores are naked, and distributed either singly or in clusters over the surface of the frond.

Our next genus—Punctaria—contains a few British species with a shield-shaped root, and a flat, membranous, undivided frond, without a midrib, and having the spores disposed as minute dots over the surface. A plantain-like species (P. plantaginea) has broad, leathery, lanceolate fronds, of a dark olive-brown colour, usually from six inches to a foot in length. Two other weeds—the broad-leaved P. latifolia of the tide pools, and the slender, tufted P. tenuissima, which is parasitic on Zostera and soe algÆ, are sometimes regarded as mere varieties of P. plantaginea.

In the genus Asperococcus the root is shield-shaped, and the frond is a membranous tubular sac of two distinct layers. The colour is pale green, and the general appearance very similar to that of Ulva. The spores are arranged in small oblong clusters which appear as dark dots on the surface of the frond. A. compressus has slightly swollen flat fronds of a linear lanceolate form, tapering below. It grows in deep water, but is often washed up during storms. A second species—A. Turneri—has large, puffy, green fronds, contracted at intervals, and grows in tufts on rocks between the tide-marks, being specially partial to muddy shores. The genus also includes the prickly A. echinatus, the long, thin fronds of which grow in dense tufts in deep water.

The last genus of the order is Litosiphon, a parasitic group characterised by a cylindrical, cartilaginous, unbranched frond, with scattered, naked spores. A very small species (L. pusillus) with tufted green fronds grows parasitic on the fronds of Chorda and the stems of Laminaria. It is only two or three inches long, has a reticulated surface, and is covered with minute jointed fibres. A still smaller species (L. laminariÆ), seldom exceeding half an inch in length, forms brown tufts on Alaria, and the rounded apex of its frond is covered with minute fibres.

The order LaminariaceÆ contains olive, inarticulate algÆ, mostly of large size, and generally growing in deep water beyond the tide-marks. Their spores are superficial, either covering the whole surface of the frond or collected into indefinite cloudy patches.

The typical genus (Laminaria) is characterised by flat leathery, ribless fronds, either simple or cleft, and supported on a stem which is often very thick and strong. The old laminÆ fall off every year, and are replaced by new fronds. The well-known Tangle or Sea Girdle (L. digitata), is a very common species on the rocks just beyond low-water mark. It has a very thick, solid, cylindrical stem, and an oblong leathery frond which is entire when young but deeply cleft later. Small specimens may be found just above low-water mark, but fine large ones are commonly washed up on the beach. Although this weed may not be regarded as an acquisition from the collector’s point of view, it will generally repay a careful examination, as it frequently bears rare parasitic species. The other common species are the Furbelows (L. bulbosa), known by its flat stem with waved margin, oblong frond cleft into narrow strips, and the hollow bulb or tuber just above the root; and the Sugared Laminaria (L. saccharina) characterised by a round solid stem, and a lanceolate, entire, membranous frond. The last species is the one most commonly used by the sea-side cottager as a weather indicator.

Alaria esculenta is an edible species known as the Badderlocks in Scotland, and also locally as the Henware, Honeyware, and the Murlins. It has a fibrous root, and a stalked, lanceolate, entire frond with a distinct midrib throughout. The stem is winged with finger-like leaflets, in which the spores are arranged in oblong clusters.

Fig. 270.—Alaria esculenta

In the genus Chorda the frond is a simple, cylindrical tube, divided internally by numerous transverse membranes, and the spores are distributed over the surface. The commonest species is C. filum (see Plate VIII.), the frond of which is very slimy, and often from ten to twenty feet in length. In its young state it is covered with gelatinous hairs, but these are worn off as the plant develops. A smaller species (C. lomentaria) is sometimes found on our shores. Its fronds are constricted at intervals, taper at the tip, and grow in tufts. It is seldom more than a foot long, and is not of a slimy nature.

The SporochnaceÆ have inarticulate, thread-like fronds, and the spores are contained in oblong, stalked receptacles, each of which is crowned with a tuft of slender jointed filaments. The typical genus contains only one British species—Sporochnus pedunculatus—and even that is by no means common. It is, however, a very pretty weed of a delicate texture and pale olive-green colour. Its stem is long and slender, pinnately branched, and the branches bear numerous small thread-like tufts.

The same order contains the genus Desmarestia, in which the frond is long and narrow, thread-like or flattened, with a tubular jointed thread running through it. Young specimens have marginal tufts of branching filaments. The species decay very rapidly after removal from the water, and should therefore be dried and mounted as quickly as possible. D. ligulata, so named from the flat, strap-like frond, is common on all our coasts. It is pinnately branched, and all the branches and branchlets taper towards both ends. D. viridis has a cylindrical, thread-like and freely-divided frond, with opposite branches and branchlets. It occurs more commonly on the northern shores.

The last order of olive-spored weeds is the FucaceÆ, some species of which are so abundant between the tide-marks, from high-water to low-water levels, that they form a very important characteristic of our shores. They are mostly large, tough, and leathery weeds, without joints, and the spores are contained in spherical receptacles embedded in the substance of the frond.

In the typical genus—Fucus—the root is a conical disc, and the frond flat or compressed and forked. Most of the species are furnished with one-celled air-vessels in the substance of the frond, and these serve to buoy up the plants and keep them more or less erect when submerged. The spore-receptacles are usually embedded near the tips of the branches, but are sometimes borne on special branches or shoots. They are filled with a slimy mucus and contain a network of jointed filaments. The weeds are very hardy, capable of withstanding long exposures to air and sun, and are sometimes to be found above high-water mark, where they are watered only by the spray of the waves for a brief period at intervals of about twelve hours. Although they are not usually looked upon as ornaments in the collector’s herbarium, they will repay examination for the tufts of smaller and more beautiful weeds to which they often give attachment and shelter.

Four species are common on our coasts, and these may be readily distinguished by the most cursory examination. The Serrated Wrack (F. serratus) has a flat, forked frond with toothed edges and a strong midrib, ranging from one to four feet long, and no air-vessels. The Knotted Wrack (F. nodosus—Plate VII.) may be known by its flattened, thick and narrow frond, without a distinct rib, from one to five feet long. The branches are narrow at the base, pointed at the tip, and are jointed to short projections on the main stem; and both these and the main stem have very large oval air-vessels. The spore-receptacles are mounted on slender stalks which arise from projections on the branches, and are of a bright yellow colour when mature. This species does not grow so near to high-water mark as do the others. Another species, the Twin-Bladder Wrack (F. vesiculosus—Plate VIII.)—is abundant everywhere along the coast, and is largely used by agriculturists both as manure and as fodder for cattle. The frond is flat, with a distinct midrib, and a non-serrated edge. Air-vessels are not always present, but when they are they usually occur in pairs, one on each side of the midrib, and are globular in form. The spore-receptacles are situated at the tips of the branches, are full of mucus, and are frequently forked. The last of the common species is the Channelled Wrack (F. canaliculatus—Plate VIII.), distinguished by a narrow frond, rounded on one side and channelled on the other. It has no midrib or air-vessels, and the fruit is contained in forked receptacles at the tips of the branches. This is the smallest of the genus, and may be found at all levels between the tide-marks. Stunted specimens may also be seen in situations where they are never submerged, but watered only by the spray of the highest tides.

The genus Himanthalia provides us with a single species (H. lorea) which is very peculiar on account of the small size of the frond as compared with the enormous dimensions of the spore-receptacles. The young frond is a pear-shaped sac which soon becomes flattened into a hollow disc. This disc then becomes solid, and concave above, and from its centre there arises a bi-forked, strap-like receptacle that often reaches a length of three or four feet, and may be mistaken for the frond of the weed by those who do not take the trouble to examine it. This weed is commonly known as the Sea Thong.

Belonging to the genus Cystoseira we have a few well-known weeds with conical disc-roots, and shrubby fronds with woody stem and alternate branches. The air-cells are in the substance of the frond, and the spore-receptacles at the tips of the branches. One of the species (C. ericoides) is of a heath-like habit, with a short, woody stem, and slender branches bearing hooked, leaf-like branchlets. Its air-cells are small, and are arranged singly near the tips of the branches; and the spore-receptacles are cylindrical, with hooked points. This weed is common on the south and west coasts, and may be readily distinguished by the beautiful iridescence it displays when in the water. C. fibrosa is very similar in general form, but is larger, and the air-vesicles are more conspicuous. It is not iridescent when in the water. A third species is named C. granulata from the rough and knobby appearance of the stem, due to numerous oval projections, from some of which spring the slender, much-divided branches. The air-vesicles are arranged in groups of two or three, and the spore-receptacles are at the ends of the branchlets. Our last example is C. foeniculacea, found on the south coast only, and readily distinguished by the numerous blunt spines that cover its long branches. The air-vesicles are narrow and pointed, and situated just below the forkings of the branchlets.

We conclude our rÉsumÉ of the British sea weeds with a short description of the Podded Sea Oak (Halidrys siliquosa), which grows in the tide pools from high-water to low-water mark, the specimens inhabiting the shallow pools being only a few inches long, while those that grow in deep water often reach a length of three or four feet. It is an olive, shrub-like weed, with a conical, disc-like root that adheres very firmly to the rock, and a pinnately-branched frond with leaf-like branchlets. The air-vesicles are cylindrical and pod-like, divided internally into about ten cells, and the spores are contained in globular receptacles at the tips of the branchlets.

The young algologist will probably meet with many difficulties in his attempts to classify his sea weeds and name the various species in his collection. In dealing with an unknown weed we strongly recommend him to first determine the order to which it belongs. The genus should next be settled; and then, if possible, the species. It must be remembered, however, that he who has made himself acquainted with the principles of classification has done good work, and that it is far better to be able to arrange the weeds into properly-classified groups than to merely learn the names of the different species without regard to the relations which they bear to one another. The following table will probably assist the reader in the determination of the orders, but it must be remembered that a microscope will often be necessary for the examination of the spores and the minute structure of fronds.

CLASSIFICATION OF SEA WEEDS