THE vegetable elements and tissues which have been described form, either separately or by their combination in various ways, the organs of plants. To these we shall now pass, and consider the structure of the principal organs of the members of the vegetable kingdom.

Leaves.—Leaves in their simplest form consist of a single sheet or layer of parenchymatous cells or cellular tissue, an example of which may be found in almost any moss (Pl. III. fig. 30). The granules of chlorophyll will often be very distinctly seen in these cells. The first addition to this form of leaf is a row or two of prosenchymatous cells running longitudinally down the middle of the leaf, so as to form a rudimentary vein or nerve. In other and more highly developed leaves, the layers of cells are numerous, and traversed by bundles of wood-cells, vessels, and ducts (fibro-vascular tissue), forming the veins,—the entire surface being covered with a skin or membrane, called the epidermis.

Epider´mis (?p?, upon, d??a, skin).—This membrane is composed of one or more layers of colourless, closely packed cells (Pl. I. figs. 13 & 28), the colour it occasionally exhibits usually arising from some of the underlying cells of the leaf being seen through it, or remaining adherent to it when stripped from the leaf. It is easily separated, by making a cut in a soft leaf, and peeling it off with a fine pair of forceps, or by soaking a leaf for some time in water and then stripping it off. It must be remarked that the epidermis covers not only the leaves, but every part of the plant.

Hairs.—Arising from the epidermis are the hairs of plants. These are thread-like or filamentous prolongations of the epidermis beyond the surface of the leaf (Pl. I. fig. 12), consisting of cells arranged end to end. They are often branched, sometimes star-shaped (stellate) (fig. 28), and present great varieties in form, as shown in the figures, the plants from which these were drawn being mentioned in the Description of the Plates. Sometimes hairs terminate in a little head (Pl. I. figs. 12 c, d, e), the cell or cells composing which secrete a colouring or a viscid substance; they are then termed glandular. The hairs of plants are particularly interesting to the microscopic observer, not only on account of their curious forms, but in connexion with the remarkable phenomenon of the circulation of the cell-contents, or rotation, as it is called, observable in them. This is difficult to be perceived by any one unaccustomed to microscopic observation, because the particles by which the motion of the cell-contents becomes evident are exceedingly minute; but practice in the use of a high power will overcome this difficulty. The hairs which exhibit the phenomenon best are those of the American Spiderwort (Tradescan´tia Virgin´ica), which is to be found in every garden. It may, perhaps be recognized thus:—The plant is about a foot and a half high; the leaves are sword-shaped and channelled, and the flowers are purple, in heads, and 1½ inch in diameter. The hairs are attached to the sides of the stamens, towards the lower part or base. The stamens should be carefully picked off with forceps, and placed on a slide in a drop of water; the hairs should then be separated with the mounted needles, and a cover applied. Under a low power, the hairs are seen to be beaded or monil´iform (monÍle, a necklace), and of a fine purple colour (Pl. I. fig. 22). On applying a high power, as the ¼-inch, the individual cells will come distinctly into view, and the nucleus will be seen very clearly as a roundish granular mass (Pl. I. fig. 23 a). On carefully examining the cell-contents, delicate lines will be observed radiating irregularly from the nucleus, some passing to the top of the cells, while others run towards its base, as in the figure; and on very close inspection, the portions of protoplasm of which these lines consist, will be found to move slowly and steadily, the motion becoming perceptible by means of the minute granules of which the protoplasm consists. The currents return at the ends of the cell, there being no passage of the contents of one cell into the cavity of either of those adjacent. During this examination, it will be noticed that the surface of the cell-wall is striated with fine wrinkles.

It may be remarked that the hairs should be taken from flowers which have only just opened; for this curious and inexplicable rotation is connected with the growth of the cell; and when this has attained maturity, it no longer occurs. The phenomenon may be observed in many other hairs of plants, as those of common groundsel (SenÉcio vulgÁris) (Pl. I. fig. 12 a, b), and in the cells of the leaves of some water-plants; but I must refer to the article “Rotation” in the Dictionary for further information.

The most important variety of hair is that derived from the Cotton-plant (a kind of Mallow), and forming the cotton of commerce. These hairs spring from the epidermis of the seeds. The cells composing it are very long and soft, becoming flaccid and easily bent when dry (Pl. IX. fig. 13).

Stings.—Stinging hairs or stings may be well illustrated by reference to the common large nettle (UrtÍca dioÍca). In this plant they consist of a thick-walled cell, bulbous at the base, which is imbedded in the epidermis (Pl. I. fig. 21), the pointed end being terminated by a very minute dilatation or knob. The sting contains an acrid liquid, which escapes when the little knob is broken off in wounding the skin, and produces the well-known irritation. By the side of the figure of the sting is represented the point of a fine needle (fig. 20), showing that the expression “sharp as a needle” has no force when microscopic bodies are in question.

Stom´ata (st?a, mouth).—On viewing a strip of epidermis, the observer will be sure to notice certain oval or roundish bodies (Pl. I. fig. 13 a), composed of mostly two kidney-shaped cells in apposition but leaving a chink between them; these are the stomata. They communicate beneath with the intercellular passages, of which they may be considered the mouths; and by their agency a direct communication is established between these passages and the air. The two cells which guard the orifice are termed the “guard cells.”

Stomata are most numerous on the under surface of leaves; they are entirely absent in plants growing under water, and in most of the lower plants. In many of the stomata, viewed in the ordinary way, the air situated between the guard cells is indicated by the black spot or dot present; but after a time, or by the application of a gentle heat to the slide, the air becomes displaced by the water, and their structure becomes very distinct.

In certain plants, the epidermis is imbued with flint or sil´ica; so that even when burnt to an ash the stomata are still quite distinct. Examples of this may be found in the stalk or culm of grasses, as in straw, the shining epidermis of which is siliceous; or the epidermis of canes. Among the lower plants, this peculiarity is especially curious in the species of EquisÉtum, or mares’-tails.

The manner in which the veins of leaves are arranged is worthy of special attention, as it forms one of the characters by which the two leading divisions of the Vegetable Kingdom are characterized. Thus in one of these divisions the veins are branched, so as to form a network throughout the leaf; the plants with these netted veins, to which belong our trees, shrubs, and most herbs, are the DicotylÉdons, or Ex´ogens; while in the second division, the veins run parallel to each other, being little or not at all branched, and not forming a network. The plants with parallel veins, among which are our grasses, lilies, &c., are the MonocotylÉdons or En´dogens.

Stems.—In the stems of plants, the tissues are arranged round a centre; otherwise, in the simpler and lower plants, they agree in structure with leaves, the centre being occupied by some element of fibro-vascular tissue, as simple wood-cells, a few vessels or ducts.

In the higher or flowering plants, the stem exists in two distinct forms, corresponding to the differences above noticed in the arrangement of the veins of the leaves; these must be considered separately.

In the Dicotyledons or Exogens (Pl. I. fig. 36), the centre of the stem, in a transverse section, is seen to be occupied by the pith or medulla, which is represented in the figure by the innermost circle. Immediately outside and around this is a narrow ring, indicating the section of a sheath to the pith, and called the medullary sheath. Next comes a broad ring of wood of the first year’s growth (fig. 36 a), traversed, from the pith to the bark, by wedge-shaped paler rays, termed the medullary rays. Outside the first year’s wood is the newer and paler wood of the second year (b); and so on, a new ring of wood being added outside the preceding layer for each year of growth of the stem.

On the outer side of the wood is the inner bark or liber (fig. 36 c); and outside this is the spongy outer bark (d), covered by its epidermis.

These structures are of different composition, as may be best seen in longitudinal sections. The pith and the medullary rays consist of cellular tissue, the cells being mostly rounded in the former, and more closely pressed together and squarish in the latter. The medullary sheath consists of vascular tissue; and the wood, of wood-cells traversed longitudinally by bundles of vascular tissue and ducts, the latter being larger and more distinct towards its outer boundary. The liber is composed of woody fibre, and the outer bark of cellular tissue.

The new woody matter being deposited outside the old, between the bark and the previously formed layer, gives origin to the term exogen (???, outside, ?e????, to produce). These structures may be examined in the section of a branch of the lime-tree or lilac.

In the Monocotyledons or Endogens (Pl. I. fig. 37), there is no distinct bark, nor pith, nor medullary rays—the entire stem consisting of cellular tissue with isolated bundles of fibro-vascular tissue scattered through it. Moreover the new substance is added to the centre of the stem, or within the old; hence the term endogen (??d??, within, ?e????). A section of a piece of cane will exhibit this structure.

To examine the structure of stems, sections must be made in various directions. The relative position of the component parts of a stem are best seen in a transverse section; but the structure of the tissues is most evident in longitudinal sections, and under the higher powers. The annual rings of the Exogens are best observed in transversely sawn-off pieces of perfectly dry stems, which have been polished with sandpaper, and varnished with spirit varnish.

Roots.—The structure of roots is very similar to that of stems; there is, however, no distinct pith, nor are there stomata on the epidermis; and the vessels are replaced by ducts. The very fine rootlets or radicles of water-plants often show the rotation of the protoplasm very distinctly.

Flowers.—The various parts of flowers, being each a modified leaf, present the same general structure as the latter. As the reader may not be acquainted with the names of these parts or organs in the higher plants, and as we shall have to compare them with their representatives in the lower forms of vegetable life, it will be well briefly to indicate them. A common and beautiful yet despised flower (Pl. I. fig. 32) may serve for illustration; this is chickweed (StellÁria mÉdia), which can be found everywhere. The outermost circle of flower-leaves, which forms a kind of cup to the rest of the flower (a), is the calyx; the separate leaves being called the sepals. The row within this, in most flowers consisting of brilliantly coloured pieces, forms the corolla (b); the individual pieces being the petals. When the two kinds are equally coloured, or not distinguishable, the whole is called the perianth, as in a tulip. When the segments of the perianth are dry and chaffy, as in the flowers of grasses, the outermost are said to constitute the glumes, and the innermost the paleÆ. Within the ring of petals are certain thread-like organs called stamens (c); and these consist of a filament (fig. 39 a), surmounted at the top or apex by the anther (fig. 39 b), which is usually coloured, and consists of two lobes. The anthers when ripe burst, and discharge a coloured dust; this is the pollen. Lastly, within the stamens is the central organ of the flower, the pistil, and sometimes there are several of them. The pistil consists of three parts, viz. a swollen base, the ovary (fig. 41 b), surmounted by a column or style (fig. 41 a), and which is crowned by a viscid and often hairy summit, the stigma (fig. 40*). In chickweed there are 3 styles.

It must be remarked that, in the flowers of some plants, stamens alone are present, while others contain pistils only, although most flowers contain both organs. When the stamens and pistils occur in separate flowers on the same plant, the plant is said to be monoecious (????, single, ?????, family); when all the flowers of distinct plants contain either stamens only or pistils only, the plant is dioecious (d??, twice, ?????); and when the stamens and pistils occur together in all the flowers of the same plant, the plant is said to be hermaphrodite. These terms had their origin in the idea that the differences of plants in respect to these organs were analogous to those of the sexes in animals. All the parts of a flower have their special uses: thus the calyx and corolla protect the delicate organs enclosed by them, until they attain maturity. The petals also, by their brilliant colours, attract insects which feed upon or collect the honey of the flowers; these at the same time conveying the pollen which adheres to their bodies from one flower to the stigma of another. The stamens and pistils are organs of fructification, it being essential for the fertilization of the flowers that the pollen should come into contact with the stigma. We will now consider some interesting points of structure in these organs.

Petals.—The petals often form most beautiful microscopic objects, on account of the curious shape and structure of the cells of their epidermis, and the splendid tints of the colouring matters contained in them. As petals are mostly too thick to allow of the cells being distinctly seen in the entire state, a little cut should be made in them while gently stretched on the finger, and the epidermis carefully stripped off with forceps; the strip should then be laid on the slide in water as usual: in this way the curious patterns of the epidermic cells will become very distinct. The petals of a red geranium (PelargÓnium) may be used to illustrate them (Pl. I. fig. 24). The structure may be best understood by reference to the epidermis of the leaf of a geranium (Pl. I. fig. 13), in which the cells present wavy or undulate walls. In the petal (fig. 24), the walls are inflexed at tolerably regular distances, so as to give rise to the appearance of a row of teeth lining the cell. If the strip of petal be folded, so as to exhibit the side view, it will also be seen that the cells project outwards from the surface to form a bluntish point or papilla, or the petals are papillose as it is called; and the surface of the membrane around the papillÆ is finely wrinkled, so as to present the appearance of very delicate radiating lines or striÆ. Intermediate degrees of this inflexion may be found in various flowers, between the slight condition seen in fig. 13 and the extreme state of fig. 24, as in the snapdragon (AntirrhÍnum mÁjus).

Anthers.—The cavities of the anthers are lined with fibro-cellular tissue, the fibres of which aid in discharging the pollen; this may be seen by dissecting an anther of London pride (Saxif´raga umbrÓsa), or of a wallflower (Cheiran´thus cheÍri) in water. It also exists in chickweed.

Pollen.—The pollen consists of minute grains called the pollen-granules. They may be viewed either in the dry state as opake objects, or when immersed in water as transparent objects. As it is often difficult to moisten them, they may be touched on the slide with a little spirit, and then a drop of water added. Their forms are very varied and curious, but they are difficult of observation from their minute size. They consist of one or more coloured cells, and these cells are remarkable for their surfaces exhibiting spines, networks, folds, and markings of various kinds. Thus in the primrose the pollen-granules are cylindrical, the surface being furrowed (Pl. I. fig. 16); in the sunflower the granules are spherical, and covered with tubercles surmounted by spines (fig. 17); in the garden convolvulus the surface of the spherical granules is covered with an elegant network, in the meshes of which are also situated spines (fig. 18); and in the granules of chickweed the surface presents pits, with minute tubercles in the centre (figs. 30 & 31). The pollen-granules are often considerably altered by immersion in water; so that, in judging of their structure when examined in water, the resulting alteration must be taken into account.

When ripe pollen-granules have been immersed in water for a short time, one or more minute tubes will be seen protruding from their surface; these are the pollen-tubes, and the granular protoplasm contained in them is called the fovil´la. In the process of fertilization of the flower, the pollen-granules fall upon the viscid stigma; the pollen-tubes are then protruded, and, passing down the intercellular spaces of the style (Pl. I. fig. 14), enter an aperture in the ovule or young seed, which is thus endowed with the power of growing into a new plant. The pollen-tubes are often very long, and they do not exist fully developed in the pollen-granules, but grow down the style, just as the little rootlet of a seed grows into the soil. The style of a crocus will serve for dissecting out with mounted needles the long and very slender pollen-tube (Pl. I. fig. 15).

O´vary.—The ovary by its growth and enlargement becomes the fruit. There are many interesting microscopic structures to be found in fruits and the seeds they contain, a few of which may be noticed here.

On examining the surface of the rind or pericarp (pe??, around, ?a?p??, fruit) of an orange, little dots will be seen, paler than the rest of the surface. These are receptacles of secretion, or glands, containing the evaporable or volatile oil upon which the fragrance of the orange depends. They consist of loose cells, surrounding a central cavity, and are imbedded in the rind.

Other receptacles of secretion, called vittÆ (vitta, a band), occur in the wall (pericarp) of the fruit of the UmbelliferÆ, or Parsley Order of plants, and their arrangement forms characters for distinguishing the genera. They may be well seen in caraway-seeds; for the caraway-plant is one of the UmbelliferÆ. It must be observed that a caraway “seed” is not really a seed, but consists of half the fruit; for, on careful examination, one side of it will be found to be flattened, the flattening resulting from the mutual pressure of the two half-fruits at that part; moreover the dried style exists at its summit. In the figure (Pl. I. fig. 19), the flattened part of the seed is next the observer. The seed has five evident longitudinal ridges, one at each corner or angle. The vittÆ are dark-coloured (fig. 19 a), and placed one between each pair of these ridges; and they consist of long flattened spaces in the substance of the pericarp, with transverse markings, indicating internal cross partitions. In botanical works, the presence of five ridges, with single vittÆ in the intervals, is given as a character by which the half-fruits (carpels) of the caraway are to be distinguished. But on closely inspecting the flattened surface, another ridge is seen running down its middle; so that the seed really has six ridges, one of which is smaller than the rest from the pressure of the other half. Hence the character of five ridges with single vittÆ is incorrect.

The vittÆ contain the volatile oil to which the fragrance and pungency of the fruit is owing, although some of the oil exists also in the cells of the kernel or albÚmen, which forms the white and greater part of the seed.

The skin of a reddish apple, peeled off in the manner described for petals, exhibits beautifully the red colouring matter of different tints in adjacent cells, while the pulp displays the cell-contents, as already mentioned. The latter may also be easily examined, from their large size, in most of the softer fruits, as that of the snowberry or the cucumber.

As the ovary or fruit approaches maturity, the petals and stamens wither and fall off, the calyx often remaining, and being sometimes adherent to the ovary, at others free or unattached to it.

Seeds.—During the ripening of the fruit, the seeds contained within it are gradually becoming further developed.

The seeds themselves are covered outside by a skin or coat called the testa (testa, a shell). This is remarkable for frequently displaying various kinds of figured patterns, consisting of raised networks, ridges, little knobs or tubercles, &c. Examples of these may be found in the seeds of the poppy (Pl. I. fig. 27), mignonette (fig. 29), and chickweed (fig. 51).

Some seeds are winged, as it is called, i. e. furnished with an extension of the testa beyond the margin of the seed. This not unfrequently consists of aggregated fibre-cells, the spiral fibre being very distinct, as in the seeds of Eccremocar´pus scÁber (Pl. I. fig. 52). In the seeds of another curious plant in this respect, viz. CollÓmia grandiflÓra, the fibre-cells are separate, so as to resemble hairs, and very mucilaginous, and in the dry seed are closely pressed to its surface. If a portion of the testa of these seeds, which can be procured at the seed-shops, be cut off, laid on a slide, a cover applied, and when the object is in focus, a drop of water be added, in a short time water softens the mucilaginous walls of the cells, the power of the spiral fibres comes into play, and the cells expand so as to form a very interesting object; the cells, in their expansion, apparently writhing like so many minute worms (Pl. I. fig. 35).

The seed itself, which is contained within the testa or seed-coat, consists essentially of the young plant or embryo. This is composed of three parts, viz. the plÚmule (plumula, a little feather), or the young stem; the rad´icle (radicula, a little root), or the young root; and one or two, rarely more, imperfectly developed or rudimentary leaves, the cotyle´dons (??t???d??, a cup).

These structures are closely packed in the seed, and are not easily recognized at first. By keeping seeds moist for a day or two until they begin to grow, or germinate as the seed-growth is called, they are readily detected, and may then be more easily found in the dry seed.

When somewhat advanced in growth, they are familiar to every one, although they may not be recognized by their names. In table “mustard and cress,” the whole consists of these organs of the two plants; the white stalk directed downwards being the radicle, the two green leaf-like lobes the cotyledons, and between the latter directed upwards is the very minute plumule, which is more easily seen when the plants have been allowed to grow larger. This structure of the seed is important to be known, because the absence or presence and the number of cotyledons afford characters, corresponding with those already mentioned in respect to the veins of the leaves and the structure of the stem, for distinguishing the great divisions of the Vegetable Kingdom. Thus, the Exogens are Dicotyledons (d??, twice), their seeds having two cotyledons; while the Endogens are Monocotyledons (????, single), having one only; and the Cryptogam´ic plants are Acotyledons (a, without), their seeds (spores) having none of these organs.

Some seeds consist entirely of the embryo, surrounded by the testa. But in many others there is also present a usually whitish, firm cellular substance, called the albÚmen (albumen, white of egg).

The albumen of seeds often affords good specimens of secondary deposit, the cells being almost entirely filled with it. An example may be found in a section of vegetable ivory, of which ornaments are sometimes made; its structure resembles essentially that of the plum-stone. In other instances the cells contain secreted matters, as starch, oil, &c.; and sometimes the cotyledons also contain starch and oil. An example of the former exists in the albumen of wheat; and of the latter, in the horse-chestnut, the filbert, and mustard-seed.

The albumen and cotyledons serve to supply the embryo with nutriment until the roots have grown sufficiently to enable them to absorb it from the soil; the cotyledons also serve as temporary leaves.

The form and relative position of the radicle and cotyledons serve to distinguish certain groups of plants. This may be illustrated by the natural order CruciferÆ, or that containing the mustard, wall-flower, &c.

Thus, in one group, which may be represented by the wall-flower, the cotyledons are flat or plane (Pl. I. figs. 43 & 44), the radicle being applied to their edges. This is best seen in a transverse section (fig. 43). They are then called accum´bent (accumbo, to lie against); and the botanical sign is O=. In the second group, the cotyledons are plane (Pl. I. fig. 38), with the radicle applied to the back of one of them, as in the seed of the common shepherd’s purse (Capsel´la bur´sa pastÓris) (Pl. VII. fig. 19). They are then termed in´cumbent (incumbo, to lie upon), and the sign is O"". While in the third group the cotyledons are folded in the middle, like the leaves of a book (Pl. I. figs. 49 & 50), and the radicle is enclosed between them, as in the white mustard (Sina´pis alba). The cotyledons are then called condu´plicate (conduplico, to fold); and their sign is O> >.

The plants above-mentioned are evidently all Dicotyledonous, or their seeds have two cotyledons; and they contain no albumen.

In the Monocotyledonous division, which may be represented by a grain of wheat (Pl. I. fig. 53), the single cotyledon forms a minute sheath (a), enclosing the plumule (b), the radicle (c) being here but little developed at first, the greater part of the grain consisting of the albumen (d); the grain should be softened in water before examination. In the germinated grain the cotyledon appears as a pale sheath, surrounding the convolute green leaves of the plumule; which may be best seen in a transverse section (Pl. I. fig. 48).

Fertilization.—A few words must now be said regarding the formation of seeds, and the action of the pollen-tubes in the process of fertilization.

In the earliest stages of growth, the young seeds, or ovules as they are called, appear as little buds, arising from the inner wall of the ovary; and the part from which they arise is called the placen´ta (placenta, a cake). In chickweed (Pl. I. fig. 41 c), the placenta forms a central column; and when the ovules are a little older, they are found to have separated somewhat from the placenta, but retaining a connexion by means of a little cord or stalk, termed the funic´ulus (funis, a cord). The ovules may be readily found in the ovary or young pod of a wall-flower, the placentas forming four lines, running longitudinally down the interior of the pod.

In this early condition the ovule consists of a mass of cellular tissue; and as new formations are soon added to it, it is termed in this state the nÚcleus. Around the nucleus are then formed two coats, an outer, called the prÍmine, and an inner, termed the secun´dine. These coats or membranes are open at one end, so as to leave a passage down to the apex of the nucleus; the opening is called the forÁmen. These structures are well seen in the ovule of the wall-flower (Pl. I. fig. 54), the foramen in the figure being indicated by a *; it will be noticed also that the funiculus runs down one side of the ovule, so as to terminate at the bottom or base of the nucleus. In ripe seeds, the spot at which the funiculus has been attached is mostly perceptible in the form of a scar. The slight prominence of the foramen can also often be distinguished, as in the seed of chickweed (Pl. I. fig. 51*); in the ripe seed the foramen is termed the mÍcropyle, and towards it the radicle of the embryo is always directed.

One of the cells of the nucleus near its apex then enlarges, so as to form a sac, called the embryo-sac. This is excessively thin and transparent (Pl. I. figs. 45 b & 47); and in it, also at the end next the foramen, one or more (in the chickweed one) smaller cells are formed from the cell-contents of the embryo-sac, which are called the embryonal vesicles (Pl. I. fig. 45 a).

Thus far developed, the embryo exists prior to the expansion of the flower and the discharge of the pollen. The embryo-sac is not figured in this early condition, the embryonal vesicle being then smaller than that in fig. 45 b, although occupying the same position.

When the pollen has escaped from the anthers and fallen upon the stigma, the pollen-tubes growing down the intercellular passages of the style, enter the foramen of the ovule, and so reach the apex of the nucleus, at which the embryonal vesicle contained in the embryo-sac is situated. The end of the pollen-tube then adheres to the embryonal vesicle, and such interchange of cell-contents takes place between them as effects fertilization.

The process of cell-formation in the fertilized embryonal vesicle then takes place rapidly, new cells being formed by the division of its cell-contents (Pl. I. fig. 45 a); and it will be noticed that the new cells are formed at the end of the embryonal vesicle, opposite to that situated at the apex of the embryo-sac. As the cell-division and formation proceed further, a mass of new cells is produced (Pl. I. figs. 46 c & 47), forming the rudimentary embryo; and from this, by further growth, the perfected embryo (fig. 55) results; or, to use a fashionable technical term, the simply cellular embryonic mass becomes differentiated into the radicle, cotyledons, and plumule, forming the embryo. It will be remarked that the position of the embryo in fig. 55 is the reverse of that in figs. 46 & 47, the radicle in the former being directed downwards, whilst that of the embryo in the figure of the embryo-sac (fig. 47) is directed upwards.

The embryonal structures are very difficult of detection; but it happens that in our little chickweed they are more easily dissected out than in most other plants. For this purpose, the ovules, placed on a slide and lying in water, should be picked to pieces with the mounted needles, under the simple microscope. They may be preserved in chloride of calcium or glycerine.

A clear distinction must be drawn between seeds, which result from the process of fertilization, and buds, which are formed independently of this process. Both consist essentially of embryo plants; but while the former originate from a single cell, the latter are outgrowths of a parent stem, from which their tissues are derived; and while the former propagate the species, the latter increase the individual.

The obvious use of seeds is the distribution of the species by the formation of new individuals.

In the general outline which has been given of the elements, tissues, and organs of plants, they have been examined principally as existing in the higher groups, or those of more complex structure; and to enter further upon a description of these plants would involve the consideration of variations in the form and arrangement of the organs of which they are composed. As these can mostly be investigated without the use of the microscope, we must pass to those in which the entire plant consists of little more than simple or parenchymatous cells, and in which the representatives of the flower are so inconspicuous, or are reduced to so elementary a condition, that the plants included in the Division have been termed Cryptogam´ic (???pt??, concealed, ????, union—figuratively for reproductive organs) or Flowerless Plants. The reproductive organs of the Cryptogamia are usually termed the fructification, implying that they produce fruit, but not flowers.