PLANTS AND ANIMALS—STRUCTURE OF PLANTS—FLOWERING PLANTS—THE STEM—THE LEAVES—FORMS OF LEAVES.

Biology is derived from the Greek word Bios, “life,” and logein, “to speak,” and constitutes the science of Organic Life. This science is divided into two branches: Botany, relating to the life of plants; Zoology, to the animals.

Plants, then, are living things, and as we proceed we shall find them born, or “germinating,” growing up as young plants, maturing as adults, and finally dying, and their particles resolving into their elements. There is more than one application of the text, “Man is but as a flower of the field.”

In the Geological section we noticed the progressive stages of the vegetable creation, and if we turn back to those pages wherein the various epochs of the earth’s formation are enumerated, we shall see how plant-life developed. Thus we find in the Cambrian the first traces of vegetable life in the weeds of primeval seas. The Silurian strata and the Devonian furnish us with many fossils of marine algÆ, and if we examine the succeeding periods we shall find a progressive increase and development; pines and tree-ferns in the sandstone, and most of the plants (by which term we include all varieties) were different from those at present existing in the earth.

We spoke of climate lately, and referred to the vegetation having an influence upon it. The same is true of the effect of climate upon vegetation. The conditions of plant-life depend upon climate, as it partly depends upon plant-life. But of all the necessary conditions the first created thing is the most necessary—light. Without light the plant is nothing.

Plants have many points of similarity with animals. They live, they possess organs, their compositions contain similar substances, such as carbon and albumen, and close chemical analyses have found the existence of the elements oxygen, nitrogen, hydrogen, and carbon in animals and plants. Therefore water must play a conspicuous part in all. Professor Huxley puts this question in his usual clear fashion. He says:—

“It is a very remarkable fact that not only are such substances as albumen, gluten, fibrin, and syntonin known exclusively as products of animal and vegetable bodies, but that every animal and every plant at all periods of its existence contains one or other of them, though in other respects the composition of living bodies may vary indefinitely. Thus some plants contain neither starch nor cellulose, though these substances are found in some animals; while many animals contain no horny matter and no gelatine-yielding substance. So that the matter which appears to be the essential foundation of both the animal and the plant, is the proteid united with water, though it is probable that in all animals and plants these are associated with more or less fatty and amyloid (starchy and saccharine) substances, and with very small quantities of certain mineral bodies, of which the most important appear to be phosphorus, iron, lime, and potash. Thus there is a substance composed of water, plus proteids, plus fat, plus amyloids, plus mineral matters, which are found in all animals and plants. When these are alive this substance is termed Protoplasm.”

We have taken the liberty to extract the above paragraph, as it expresses in a few words, and very clearly, the common origin of plants and animals. We will now consider the conditions of plant life. Heat, light, and moisture are the principal necessaries, with of course air and certain earthy matter. Some plants, like some few animals, live in darkness, such as truffles and fungi, as do cave-fish and bats. But this is the exception, and the sense in which plants (or animals) can exist without light is a very restricted one, and only to be sustained at the expense of the plant material, which must originally have been derived by the action of light. Light, therefore, is the great “producer.” It gives life to plants upon which animals feed, and therefore light is in one sense the beginning of all things. We can now understand why light must have been created first.

Many interesting experiments can be made to observe the effect of darkness and different coloured light (transmitted through coloured glasses) upon plants; and it will be observed that although the leaves may not develop the natural green tint, the flowers will exhibit their usual colour. One effect of light upon plants is to make them green.

We all admire the beautiful green of the spring leaves, and the freshness of the colours of the trees and grass. But if we pluck up a plant its root is not green. Why then is the cleaned root not as green as the upper portion?—Because of the absence of light. There is a substance called Chlorophyl which, when acted upon by light, becomes green. This is contained in plants, and when the daylight falls upon it the substance turns green. So, as we said above, plants are not green when kept in the dark. Celery is a common instance. Heat, of course, has much to do with the activity or vitality of plants, and the range extends from just above freezing point to 122° Fahr. We find tiny plants blossoming in Alpine regions close to the snow, and others in full life in the tropics, protected from the fierce rays by scaly coverings and huge leaves. In the northern regions buds appear as soon as the surface warmth is felt, and even when no heat can yet penetrate to the roots. Thus we see that Nature fits the animal and the plant to the localities in which they live, and they exist interdependently. Some can defy cold, others flourish in drought; some love moisture, others live in great heat encased in prickly armour.

With this introduction to biology we may now pass on to speak of the seeds and germination of plants, which we divide into the flowering and non-flowering species. We suppose that the appearance of various organs of plants are familiar to our readers, and the root, the stem, the leaves, and the flower itself, as well as the seeds, are well known, and their uses understood generally.

Now if we compare a mineral—say a crystal of quartz—with a plant, we find the crystal uniform, consisting of small particles of quartz throughout, and it appears an aggregation from outside of these particles in a particular form. It cannot grow from within. But a plant can; and it is very different in structure and appearance. It receives nourishment from outside also, but it assimilates the materials, which are not the same as those we meet with in the plant itself. The mineral, on the contrary, is essentially the same throughout; it can only grow by aggregation of atoms like itself. A plant, therefore, like an animal, must have organs within it, and must be capable of change in itself; it has powers of reproduction, and in some few instances of locomotion; it can eat flies, and assimilate them as an animal does.

A plant, therefore, is an organized body without external voluntary movement; and hereby it is essentially distinct from an animal, with which, in organization, it is closely connected. The simplest form of the animal as of the plant, is that of a minute vesicle or cell, containing a fluid in which are some granular substances. At this stage it could not be distinguished from the simplest plant, if it had not the faculty of voluntary movement—the power of changing its place. The animal has a locomotive power. Sometimes, indeed, it is a very limited sphere to which it is confined; yet it may change its place for another more conducive to the exigencies of its being.

It is sufficient for the present to have given the most general characteristics by which plants are distinguished from the other objects that, with them, compose the great kingdom of Nature. A precise and clear apprehension of their varied forms and wonderful phenomena can only be obtained by a careful analysis of the nature and structure of the subjects of the vegetable kingdom.

The cell is the fundamental or elementary organ of plants, and the knowledge of its metamorphoses and functions constitutes the foundation of botany. We must therefore first consider the simple organs of plants.

Structure of Plants.

It will be necessary for the reader to gain some little knowledge of the tissues and cells of plants before he proceeds to examine the organs of development, and a microscopic examination will soon disclose the few simple tissues which are termed cells and vessels. These exist in all plants of whatever nature. Plants are aggregations of cells, “every one of which has its little particle of protoplasm enclosed by a casing of the substance called cellulose, a non-nitrogenous substance nearly allied in chemical composition to starch.”35 The tissues are “cellular” and “vascular” respectively.

The cells have an outer sac or covering which is transparent, and this cover is the cellulose above mentioned. It contains (1) the protoplasm, a kind of jelly-like substance (which holds the proteine or basis of life); (2) water or cell-sap; (3) the nucleus; and (4) chlorophyl. This protoplasm is apparent in both plants and animals. The cells containing these various substances—in which we find oxygen, hydrogen, nitrogen, sulphur, and carbon, with phosphorus perhaps—are divided to form new cells, and so on with most astonishing rapidity, amounting in some instances to millions in a day, and a case of this nature will readily be recognized in the mushroom.

Cellular tissue is composed of these cells, and vascular tissue is composed of vessels or tubes like coiled springs, which are cells without divisions or partitions. These tissues will be referred to farther on as dotted ducts or tubes.

In most of the spongy parts of plants, as in the pulp of fruits and pith of elder, the cells preserve the globular or oval shape represented in fig. 739 A. But the cells, in consequence of that mutual pressure, more frequently assume the form of a polygon (fig. 739 B), the section of which is generally hexagonal. The cellular tissue may generally be compared to the bubbles produced by blowing through a straw or tobacco-pipe into soap and water; or it may be illustrated by placing balls of moist clay together, and then pressing them more or less strongly. In this manner every individual ball assumes a polygonal shape corresponding to the form of the cells represented in fig. 739 C, and which disposition is, in many plants, preserved with the utmost regularity. Such cells as are, with tolerable equality, extended in all directions, are named parenchyma, and of these are composed the tuberous parts of plants, as the potato, dahlia-roots, etc., and especially the soft, spongy parts of the pith, bark, leaves, etc. We frequently, however, meet with cells which are extended longitudinally, and pointed at both extremities, as in fig. 740. The sections of these cells, which are compactly arranged, have the appearance of a hexagon. They are termed woody cells, or woody tissue (prosenchyma), and constitute the chief portions of the more solid parts of plants, as the ligneous parts of trees, shrubs, etc. Very long, flexible cells, as those which constitute the fibres of flax and hemp, are called bast-cells, and appear under the microscope as round threads of uniform thickness, whereas the fibres of cotton wool, which rarely exceed one or two inches in length, when magnified, present the appearance of flattish bands with somewhat rounded margins. By these marks, the union of flax and cotton in the same web or piece of cloth may be detected.

Occasionally the cells assume very abnormal shapes, as the stellate or star-formed cells. These are described as irregular cells.

As every plant, whether small or great, is only an aggregate of a great number of cells, so, also, the life of a plant is nothing else but the sum of the activities of all the cells of which it is composed. The special province of the cells is to receive from the soil or atmosphere the water necessary for the various vegetative purposes, together with the nutritious materials dissolved in the watery and aerial fluids, and to circulate them through the whole body of the plant. The circulation within a plant is not carried on through the agency of tubular channels, but only by the passage of sap in all directions from one cell to another.

Since the cells have no openings, it is somewhat difficult to understand in what manner the fluid can enter into the plant from without, and by what means it can inwardly pass from cell to cell. This phenomenon, however, is dependent on the peculiar quality both of vegetable and animal membranes and fibres—viz., that they are permeable by many fluids, without being dissolved by them. Experiments show that this permeative action is carried on in accordance with definite laws. When two fluids of unequal densities—as, for example, an aqueous solution of sugar and mere water—are separated from each other by a diaphragm of pig’s bladder, we perceive a constant tendency on both sides to restore the equilibrium in the density of the two fluids. A portion of the water penetrates the bladder, mixing with the solution, and a portion of the latter finds its way to the former by the same medium. In this experiment one important fact is to be observed—viz., that the lighter fluid always passes through the separating medium more rapidly to the denser than vice versÂ; consequently, in this experiment more of the water passes through the bladder to the saccharine solution than of the latter to the water. This permeative capability of the tissue of vegetables and animals is called endosmose.

The cells both circulate the sap and alter its condition, so we find differing substances in the same plant. The cell as described creates new cells, and the force with which the sap rises is rather greater than the pressure of the atmosphere.

The vascular, or fibrous tissues, are illustrated in the margin (fig. 741). They usually contain air. Some plants have no vascular tissue, and are termed cellular plants—such as mushrooms, fungi, mosses, and seaweeds. Many contain both tissues, and these are the more highly developed kinds.

Sometimes we find a milky juice in plants. This is called latex; and caoutchouc is always present in it. This juice is contained in tiny tubular vessels, which have their origin in the new cellular tissue of the lactiferous plants.

The tissue of the cuticle, or epidermis, which externally covers all parts of the plant while they remain green, is of a peculiar nature, and demands special consideration. It is formed of flat tubular cells, very much compressed, and in close contact, with the exception of some parts where the stomata, or mouths, are placed. In fig. 742 a section of the leaf is represented, the large transparent empty cells of the epidermis, and above these the parenchymatous cells of the leaf filled with greenish-coloured granules. In four places (fig. 743) stomata (s s s s) are seen, which have their openings surrounded by parenchymatous cells disposed in semilunar forms. Under each stoma (mouth) there is a hollow space which is connected with the intercellular passages of the leaf. These stomata, represented in fig. 743, are so numerous on the under side of the leaf, that hundreds have been counted in the space of a square line. Through these minute organs an intimate connection exists between the interior of the plant and the external air.

The epidermal cells not unfrequently exhibit very abnormal formations. When much extended in length they appear as hairs which are frequently branched, and in many plants they contain an irritating sap (in the nettle, for example). Bristles, prickles, glands, warts, and especially the substance which forms the well-known cork, are all due to the metamorphosis of this exterior integument.

Flowering Plants.

Flowering plants have certain distinct features which cannot be mistaken, for they grow well above ground, and can easily be examined. There are a hundred-thousand different species of flowering plants, and a visitor to Kew can study them there. Any child can tell a flower when he sees it, but a flowering plant is no more restricted in Botany to actual bright blossoming plants, than the term rock in Geology means a mass of stone only. Flowering plants may be either very gorgeous or very simple; and so long as they contain a reproductive apparatus they are flowering plants. The rose is a flowering plant, but the oak is equally one. The beech tree and the primrose are classed under the same heading.

Flowering plants must possess stamens and pistils, which bring forth seeds which contain an embryo, and the germination of seeds can be easily perceived by any one who will take the trouble to soak them (say “scarlet runners”) in warm water, and keep them warm in moist flannel. The process may then be examined at leisure.

We need hardly insist, after what we have said, upon the necessity for some air and light, or remind the reader that he must not keep the seeds in a close, dark place, though light is not so necessary at first as air. The embryo connects the “cotyledons” or halves of the seed, and this develops into a tiny rootlet or “radicle,” and upwards into the stem, the commencement of which is known in botany as a “plumule.” The rootlet seeks nourishment from the ground. The albumen secreted in the cotyledons feeds the embryo, until (in some cases) it is exhausted and they die away. In other cases they grow up and obtain food for the young plant in the air. Some plants have (like wheat) only one seed-leaf, or cotyledon; and these kinds are called monocotyledons, or endogens, in which the growth is upright. The others are called dicotyledons, or exogens.

So far now, perhaps, you may understand that the outer covering of the seed is called the testa; the opening which may be perceived in the ordinary bean near the dark spot is the micropyle, or little gate; that the halves of the covering are termed cotyledons, or cups, and that the embryo sprouts upwards and downwards, the upper part of the stem being the plumule, and the lower portion the radicle. Even if the seed be put micropyle upwards into the ground, or between layers of flannel, to germinate, you will find that the radicle will always curve downwards.

The root then being displayed, it pushes its way into the ground to seek for nourishment, and when the proper moisture has been admitted to the seedling, which has been reposing in the cotyledons all the time, it sprouts up rapidly. The root and its fibrous extremities have been pushing and insinuating themselves into and through the ground, and by small knobs or suckers known as spongioles, the rootlets or fibrous parts of the root pick up sustenance for the plant, and it is then carried by tubes to the root, and so on throughout the plant, and with air ducts serve to keep the plant alive.

The stem emanates from the plumule, and in a short time little knots develop upon it, which are the incipient leaves. The knots are divided into nodes and internodes, because they appear on different sides of the stem and intermediate, so as to alternate with each other, and are really buds. The issues unite also into leaf-stalks or petioles, and extend into the leaf-frame or skeleton as we see it when the leaf has decayed. So thus we have an upward and a descending growth, which respectively constitute the stem and root of a flowering plant.

Some trees have roots growing from the stem, as in the banyan tree, and roots can produce stems as well as the latter can form roots. The uses of roots are so well understood that we need not particularize them. In many trees we find what are termed lenticellÆ, like holes in the bark. These fissures will put forth roots under favourable circumstances. These stem roots are called adventitious, and by taking “cuttings” from plants we make good use of them for propagation.

But there are underground stems as well as those which flourish and climb above it. “Bulbs” and “tubers” are common instances of these underground stems, or “rhizoma,” which are horizontal. The ordinary stems are termed “aerial” stems to distinguish them from the earthy and subterranean. The aerial roots of ivy are only used for support, and are not its proper roots, though some parasitic plants strike into the trees and are nourished by them.

The Stem.

The stem is that portion of the plant-axis which grows upwards or above ground, and may be, as we have just read, subterranean. As the great function of the root is to procure sustenance for the plant, the stem assists in carrying the nourishment through the branches and leaves. We shall find two forms of stem—the underground, or root-stock, and the stem proper. There are in these two former several varieties as under:—

1. The Bulb, which is a short globular stem surrounded by thick leaves, and producing buds—as, for example, the onion.

2. The Tuber, similar to the foregoing in shape, having no leaves, however; the potato is an instance.

3. The Rhizome (root-stock), like a root only producing buds, which roots do not. The iris will serve as an example.

The varieties of the stem-proper are:—

(1) Filiform, or thread-like, simple, or branched, as in mosses.

(2) The culno, a thin, hollow, and frequently-jointed stem.

(3) The palm or simple stem, seen in tree-ferns and palms. It is marked by the scars of dropped leaves.

(4) The stalk, very common, of a green hue, and its life is limited to a twelve-month as a rule. The so-called “stem” of the hyacinth is not a stem, it is a stalk, or flower-stalk, pushed forth for a temporary purpose.

(5) The ligneous stem is the perfected kind, and an example will be apparent in every tree.

The duration of the stem of a plant is usually the same as of the plant—so we have annuals, biennials, and perennials. The substance of the stem determines its character, so we may have it solid, or soft, hollow, tubular, flexible, rigid, or a tough stem. There are fibrous, herbaceous, and juicy stems. They may be directed uprightly, straight, procumbently, arched, or creeping, above, or underground, climbing, clinging, floating, or twining.

There are many plants with little or no stem deserving the name, as in the onion; and we must all remember when studying botany that it is not the place where a portion of a plant may be found that constitutes it a root or a stem. The form and structure should be studied, and its purpose in creation. So stems may be underground and roots above it. The root and stem, briefly treated of in the foregoing paragraphs, have certain points of resemblance, inasmuch as both consist of a main or trunk line, so to speak, from which branches diverge as “rootlets” and “twigs”; and how beautiful the latter are any one can see in a good photograph of a wintry landscape. But stems have nodes and internodes, and roots have not, and this is the great and apparent difference.

The covering of plant-stems is varied, and many instances of such clothing will occur. We have woolly stems and hairy stems, which develop into thorny ones—for thorns are only strong hairs. Spines and stings and prickles defend the stems, and keep rude hands from meddling. We will now cut the stem and see what it is composed of, and how it looks inside. We have only to cut it across and again perpendicularly to find out a great deal about the interior structure of the stems of branching plants (exogens).

The elder, from which the whistle of our boyish days is fashioned with a penknife, will serve any lad for an illustration. Inside we find what is called “pith,” which is cellular tissue. Round this is fibre, and outside is a skin, or the plant-cuticle. We may remark that the tissues of flowering plants are characteristic of the monocotyledonous and the dicotyledonous plants. Of the former we append an illustration,—a section of palm-stem,—and we find bundles of vascular tissue dispersed apparently at random amongst the cellular tissue of the parenchyma, or cellular tissue. These stems do not grow by the increase of the existing vascular tissue, but by their new production at the circumference, and so they grow in both directions, laterally and uprightly. These plants belong to the Endogens, and if Indian corn be grown we shall have full opportunity to study the formation. In cutting a fern stem we are familiar with the “oak” pattern of the matter it contains. We have few specimens of endogens in England.

The dicotyledonous stems are common to our trees and most plants, and may therefore be considered with advantage. The stem consists of the vascular tissue called “pith,” and we give an illustration of the cells magnified very considerably. The arrow indicates the outward direction (fig. 757).

We here perceive the vascular bundle proper surrounded by a very large-celled tissue, aa'bef. The almost square cells, aa', form the epidermis on which follows the less dense cellular tissue of the bark. The latter surrounds a half-moon-shaped bundle of bast-cells, c, which are separated in the direction towards the interior, by a layer of cambium, dd'd, from the bundles of vascular tissue, consisting of vessels and longitudinal cells. The latter tissues may be distinguished in the transverse section by the thicker walls, gg, and by their greater breadth, hh. It is further to be remarked that the cambium transparent tissue, dd, appears on both sides of the bundles of vascular tissue, and extends to the next bundle, and thus presents an uninterrupted circle throughout the entire circumference of the stem.

On examining the section of a one-year-old dicotyledonous stem, magnified six times, as in fig. 758, we perceive several parts clearly distinguishable from each other, corresponding with the arrangement of the bundles of vascular tissue.

Enclosed by the epidermis, a, is a large-celled tissue, b f and m, in which a number of vascular bundles form a circle. In each of these we notice that the outer portion, consisting of bast-shell, c, is separated by the cambium, d, from the inner woody portion, e. The cambium forms a closed circle which penetrates through all the vascular bundles.

In the course of the further development of the stem, the parts, a b c, constitute the bark, the vascular bundles, e, the wood, and the cellular tissue, f, its pith. The tissues, m, penetrating between the vascular bundles, are called the medullary rays. The cambium is to be regarded as the most important part, since it is the source of new bundles of vascular tissue which year by year increase the circumference of the stem.

The growth of a dicotyledonous stem is continued by the formation of a new circle of vascular bundles on the circumference of the stem in the second year. Each new bundle, as has already been shown, is produced in the cambium, and consequently is deposited between the wood and inner bark.

Thus every year a new layer is deposited between the previous formation and the bark; and a section will exhibit these concentric rings of wood obviously distinct from each other; and as one year is requisite for the formation of a single layer of wood, these depositions are named annual layers or rings. In fig. 759 we have a representation of a stem three years old, and one of five years of age.

The number of rings in the stem do not invariably agree with the number of years the tree has been growing, but it may be accepted as a rule.

The stem is the medium of communication between the roots and leaves at first; but after a year this important duty is deputed to the cambium layers of new woody tissue, etc., and as time goes on the living power has accumulated immediately under the bark. So although the tree be quite hollow it will live. The interior has been closed up by deposition of wood and has decayed; but the life functions being relegated to the bark, the old tree lives on. If we remove the rind all round a tree it will die.

The Leaves.

When in the spring the young leaves appear upon the trees, and as summer advances they become fully developed, we are all grateful for the beautifully varied tints of green, and for the shade we can so fully enjoy. The study of leaves is a most interesting and instructive one, and nobody should omit to examine them. Their forms are infinite, or, at any rate, countless; their size as varied as their forms. Many attributes of the leaf will occur to every reader, and we will briefly describe these essential organs of plants. Air and light are necessary to the development of leaves, and their principal use is to present a surface to the food material which the plant absorbs. They breathe, as it were, and absorb the carbonic acid from the atmosphere. These functions are called “assimilation,” “transpiration,” and “respiration,” which we will detail by-and-by.

Leaves are distinguished according to position and duration. Some leaves have very simple forms, others are compound, so to speak. Some are plain and rounded, others are toothed, like the holly. The skeleton of a leaf is a very interesting study, and it will show the beautiful structure of these common objects. The delicate lines of the green leaf are “veins,” or sap-vessels, which convey the necessary nourishment. The leaves are called the “embryonic” (seed-like), the radicle, or root-leaf, the stalk-leaf, and the stipules, which grow at the base of stem-leaves, and the floral leaves, which bear the flowers or fruit buds. Leaves which are developed at the end of a chief axis are termed blossoms. Of course it must be understood that all the different kinds of leaves do not occur upon the same plant. The leaf may be accepted to mean the stem-leaf.

Leaves are folded up in various ways, and the manner in which this is accomplished is termed the vernation of the plant. The leaves of endogens and exogens differ in their veining. The former veins do not touch; there is none of that beautiful interlacing which we find in the exogenous leaves. In the former the veins rise from base to apex, curving as they advance, as in the well-known lily of the valley. This “nervous system” of the leaf is its “venation,” and the veins distributed in the blade or lamina of the leaf are twofold,—as remarked,—ascending in curves, or diverging from a central nerve called the “mid-rib.” These lateral nerves are either parallel or “reticulate”—that is, net-like.

We will now examine the forms of leaves which are regulated by the divergence and extension of the divisions of the mid-rib. Thus we get an orbicular, or peltate leaf; palmate, digitate, and pedate forms also occur, as may be seen in the illustrations, pages 672 and 673, where all the varied shapes can be studied. The leaf consists of a petiole or stalk, and the lamina or blade. The petiole is composed of bundles of vascular tissue; the lamina is formed by their extension, the interstices being filled with cellular tissue. So we perceive that the leaves and stems are composed of similar materials. To defend the tissue a skin, or epidermis, is placed upon the surface of the leaf, and this epidermis is full of breathing holes, or pores, called stomates (compare page 664). There are also cells filled with chlorophyl, which gives the leaf its green tint.

The petiole may be absent in a leaf, and when it is the leaves are termed sessile, or sitting leaves. These leaves sometimes coil round the stem, and are called “amplexicaul,” or stalk embracers. These are simple leaves. Compound leaves are composed of several blades or laminÆ on a stalk, and are seldom sessile. Simple Leaves are almost innumerable in form and variety. Leaves may be equal or unequal, acicular or linear, rounded or oval, cordate or obcordate, reniform or sagittate, perfoliate or connate, crisp, whorled or truncate, retuse, acuminate or mucronate. The margins of simple leaves again are entire, deft, notched, crenated, crenulated, sinuous, or dentated. They are pinnatifid, multifid, or lobed, according to the divisions of the leaf.

Compound leaves are also divided into classes. The pinnate, as the rose-leaf, the clover trefoil. There are “doubly pinnate,” the digitate, as in the horse chestnut. Compound and simple leaves can be readily distinguished by inspection, for the former are “articulated” to the stalk and can be separated, but the simple leaves will be torn, for they are confluent throughout.

Leaves are evergreen or deciduous, accordingly as they retain or shed themselves. The ordinary leaf is deciduous; the fir and the yew and the imported laurel are evergreens. We have very few of these as natives of England, the ivy, yew, and fir being the three most common. Sometimes a plant peculiar to Killarney, and known as the arbutus, is included in the list. But the Scotch fir and the yew are distinctly native evergreens.

The detailed characteristics of leaves must be passed over until we come to the fly-catching leaves—such as Venus’ fly-trap, the droseras, and nepenthes, which appear to catch and devour insects for food. The Venus’ fly-trap may be examined, and we shall find the leaves covered with tiny and very sensitive hairs. Often a fly happens to alight upon the leaf, which is extended in a most innocent manner (see illustration). As soon as the fly settles the leaves close, and the digits lock tightly together, thus preventing the escape of the prey. The droseras, sarracenias, and nepenthes also kill their food. The sarracenias form curious cups, into which insects are enticed in search of fluid, and then, as in the case of the house-haunting cockroach, they cannot get out again. The nepenthes have a cup and lid for insect-catching, and within the cup a liquid is secreted.

We will close this portion of our subject with a quotation from a recent article upon botany referring to leaf arrangement. The writer says:—

“Efforts have been made to determine the laws to which these various modes of leaf-arrangement may be referable. The result is found in the doctrine of ‘Phyllotaxy,’ as it is called, the fundamental principle of the whole being that Nature, in the disposition of the leaves upon the stem, works upon precisely the same idea as that which is set forth so distinctly and elegantly in the common pine-cone; and, on a minor scale, in the beautiful cone of the female hop; not to mention the quasi-cones of many species of tropical palm, such as the Sagus and the Mauritia; nor to mention either, the very delicate repetition of the whole series in the florets of the Rudbeckia and the ripening fruits of Chaucer’s daisy. In every one of the flower and fruit arrangements mentioned, the idea is the spiral,—the same sweet old fashion which we have had in the twining stems of the convolvulus, the woodbine, and the scarlet bean; which comes out again in many a sea-shell, and in human ringlets; and this idea, according to ‘Phyllotaxy,’ governs the position of the leaves. Following alternate leaves up the stem, their sequence is clearly spiral. Through the non-development of internodes, they are brought closer and closer together; and even when the entire mass of foliage is concentrated and condensed into the rosulate form, as in the houseleek and the Echeverias, the spiral prototype is still distinguishable. The whole matter has been reduced to one of arithmetical exactitude; and for those who love calculations and “fractions,” the determination of the spirals, their continuity and intermixture, supplies abundance of curious entertainment. All three modes of leaf-arrangement are found in certain herbaceous plants, none disclosing this particular kind of playfulness more plainly than the common pyramidal Loosestrife, Lysimachia vulgaris, and the purple Lythrum of the waterside, in each of which very handsome wild flowers, alternate, opposite, and whorled leaves may be found in near neighbourhood. Alternate and opposite leaves are also met with, side by side, in various species of MyrtaceÆ; and imperfectly, upon young shoots of the common ash-tree. The rule is, nevertheless, that there shall be uniformity, and in many of the largest natural orders the rule is never broken. In the RosaceÆ the stem leaves are invariably alternate; in the GentianaceÆ they are invariably opposite.”