PART I.

STRUCTURAL BOTANY.

CHAPTER I.

GENERAL VIEW OF THE VEGETABLE WORLD.

THE simplest plants, such as the Red Snow (Protococcus) (Fig. 1), consist of a single membranous sac, or cell, as it is termed, which in form is more or less spherical or oval. In plants immediately above these in point of complexity we find the cells still all alike, but, instead of being separated, and each form ing a distinct plant, they are joined end to end, and form a many-celled filament, which is straight or curved in various ways, as in Oscillatoria (Fig. 2). All these plants-so far, at least, as is knownmultiply by division of their cells only; but a little higher in the scale we meet with plants in which certain of their cells perform the function of nutrition, while others are set apart for the purpose of reproduction. Thus, in the

FIG. 2. Two plants of Oscillatoria spiralis.

FIG. 1.-Several Red Snow plants (Protococcus (Palmella) nivalis), magnified.

Molds, such as Mucor (Fig. 3), or Penicillium (Fig. 4), the cells, which serve as organs of nutrition, form branched, jointed filaments, or hypha (see

page 21), which lie upon the surface of the substance furnishing the plants with food; while those destined to reproduce the individual, which are called spores, are devel

2

MOLDS-THALLOPHYTES.

oped in globular cavities (sporangia), as in Mucor (Fig. 3), or are arranged in necklace-like branches at the end of special filaments, as in Penicillium (Fig. 4).

Yet a little higher in the scale of vegetable life we find the cells so combined as to form leaf-life expansions (Fig. 5), or solid axes, as well as special organs of reproduction (Fig. 5, t,t). But these cells are all more

FIG. 3.-A species of Mold (Mucor), with branched mycelium (hyphal tissue) below, from which two stalks are seen to arise, each of which is terminated by a sac (sporangium or ascus), from which a number of minute bodies (spores) are escaping. FIG. 4.-Another Mold (Penicillium glaucum), with branched mycelium (hyphal tissue), and stalk bearing several rows of cells, which are the germinating spores (conidia).'

or less alike, so that no true distinction can be drawn between the often very different looking parts we meet with

FIG. 5.-Thallus or thallome of the common Bladder Sea-weed (Fucus vesiculosus). t, t. The fructification. v, v. Bladders of air.

in such plants as a sea-weed or a mushroom. Such a combination of similar cells, whatever the precise form may be, which presents no differentiation of leaf, stem, and root, is called a thallus or thallome, and every thallus-producing plant is therefore termed a Thallophyte or Thallogen. Under the head of Thallophytes we comprise all those simpler forms of plants which are commonly known as Algæ, Lichens, and Fungi.

Again, as all Thallophytes are composed of cells, they are also termed Cellular Plants, in contradistinction to those which come above them, which are called Vascular Plants.

From the Thallophytes, by various

CRYPTOGAMOUS OR FLOWERLESS PLANTS. 3

intermediate stages, through an order of plants called the Liverworts (Figs. 6 and 7), we arrive at another orderthe Mosses.

In the Mosses the stem often contains elongated cells, which are, to a certain extent, thickened, and differ little from the true wood-cells met with in higher plants.

Still ascending, we find in the Club-mosses, Pepper-worts, Horsetails, and Ferns, a continued advancement in complexity of structure; vessels of different kinds make their appearance for the first time; and the stems of Ferns are frequently of considerable size and height.

FIG. 6.-A portion of the flat

thalloid stem of Marchantia polymorpha, showing an antheridial receptacle, r, supported on a stalk, s.

In all the plants above mentioned we have no evident flowers as in the higher plants, hence they are called Flowerless; but their organs of reproduction are very small and inconspicuous, and therefore they are also termed Cryptogamous, that is

to say, plants with concealed or invisible reproductive organs. These Cryptogamous plants are again divided into two groups, called Cormophytes and Thallophytes; the latter group comprising the simpler forms of plants, and the former group those plants which present us with a more or less evident stem, bearing leaves, and, except the Liverworts and Mosses, also true roots and vessels of different kinds.

All plants above those called CrypFIG. 7.-Jungermannia togamous, from possessing evident flow

bidentata. The stem

is creeping, and bears ers or reproductive organs, are termed

numerous small imbri

cated leaves.

Phanerogamous, Phænogamous, or Flow

4

PHÆNOGAMOUS OR FLOWERING PLANTS.

ering. These latter plants are also reproduced by true seeds instead of spores, as is the case in all Cryptogamous plants which possess reproductive organs. A seed is essentially distinguished from a spore, by containing within itself in a rudimentary condition all the essential parts of the future plant in the form of an embryo, with a distinct central axis, the lower part of which is called the radicle and the upper the plumule. Fleshy lobes, two or one, are united to this axis, and by their number divide Phanerogamous plants into two great classes called respectively Dicotyledons and Monocotyledons. But Cryptogamous plants have no cotyledons and are hence termed Acotyledons. In germination the cotyledons afford nutrition to the developing plumule and radicle, from which the three essential organs of the plant-root, stem, and leaves—are evolved. These are the organs of nutrition, while the flower and its parts are devoted to the formation of seed, and are hence termed organs of reproduction. On the contrary, a spore merely consists of a single cell, or of two or more united, and never exhibits any distinction of parts until it begins to develop in the ordinary process of vegetation, and then only in certain cases, when a special apparatus appears designed for the purpose of reproduction.

These Phanerogamous plants also present two wellmarked divisions, called respectively the Angiospermia and the Gymnospermia: the former including those plants in which the ovules are inclosed in a case called an ovary; and the latter, such plants as the Fir, in which the ovules are naked or not inclosed in an ovary. In the Phanerogamous plant we have the highest and most perfect condition of vegetation; and it is to these that our attention will be more especially directed in the following pages.

After this general sketch we may now proceed to the description of the elementary structures or building materials of which plants are composed.