OUTLINES OF THE VEGETABLE KINGDOM. 119 



excess of water is exhaled by a process of transpiration, from little apertures 

 or mouths named stomates, found especially on the under side of the leaf ; 

 through these stomates, the leaves may also absorb vapor and gases. In the 

 leaves, also, the processes of assimilation are performed, as well as those of respi- 

 ration, which in plants is rather an assimilative than a respiratory act, con- 

 sisting essentially in the fixation of carbon, derived from carbonic acid, to- 

 gether with the elements of water and ammonia, and in the evolution of 

 oxygen. These processes occur under the influence of solar light, and in this 

 way, not only chlorophyll, the green coloring matter, but other ternary and 

 quinary constituents are prepared, such as the vegetable acids, the carbhy- 

 drates, starch, sugar, gum, cellulose, and lignin or woody fibre, and also the 

 hydrocarbons or fixed and volatile oils ; and moreover by the fixation of nitro- 

 gen or ammonia, there are formed those most important albuminoid sub- 

 stances, gluten, fibrin or legumin, which are necessary to all the growing 

 parts of plants, and which are stored up abundantly in the seed. The fluids 

 returned from the leaves, supply materials, chiefly cellulose and lignin, for the 

 formation of the new parts of the stem and roots, and so assist in building up 

 the passive framework of the plant ; and they also deposit in their path, by 

 processes of secretion, special chemical compounds, such as the essential and 

 fixed oils, and the vegetable alkaloids or bases, exemplified by quinine, mor- 

 phia, thein, caffein, and asparagin ; and finally even, it is said, throw off by 

 an excretory process, chiefly by the roots, residual substances which would be 

 injurious to the plant. The decomposition of carbonic acid, and the evolution 

 of oxygen, which takes place in the mixed assimilative and respiratory func- 

 tions of plants, are phenomena the reverse of those which occur in the respi- 

 ration of animals, and by which oxygen is absorbed and carbonic acid given 

 off'. In the germination of the seed, and at the period of perfection of the 

 flower, carbonic acid is, however, also given off by plants. In the absence of 

 light all parts of plants are said to exhale carbonic acid, which must always 

 exist in their fluids, and then escapes decomposition. In some plants, certain 

 special fluids, more secretive than nutritive, constituting the so-called latex, 

 circulate in peculiar vessels named laticiferous. The reproductive functions 

 of all the phanerogamic plants are performed by the agency of the flowers, or 

 rather by that of their most essential parts, viz., the pollen and the contents 

 of the ovule, which are brought together by the various contrivances mani- 

 fested in the structure and arrangement of the stamens, anthers, pistil, and 

 carpels. The petals and sepals of the corolla and calyx, when present, are 

 supporting, protective, ornamental, and attractive to insects, which aid in 

 conveying the pollen to the stigma ; bracts, stipules, and tendrils are also 

 efficient organs of protection and support. Buds are the means of multiplica- 

 tion by division of the individual, seeds and spores by a true reproductive pro- 

 cess. Within the fertilized ovule the embryo, with its one or two cotyledons, 

 is formed. In the cryptogamic flowerless plants, instead of a seed containing 

 an embryo, sporangia, or other organs, appear on the fronds or thallus, and 

 produce within them the so-called spores. The nutritive processes of the 

 cellular thallogens are accomplished without the aid of woody or vascular 

 parts. 



The vegetable textures of which all plants are built up, are the so-called 

 woody tissue, Fig. 47, /; the vascular or tubular tissue or ducts, c, d, e; and the 

 cellular tissue, a, b. Certain parts, such as the pith, a, the cuticle, b, and the 

 embryo of the higher plants, consist entirely of cellular tissue, i. e., of an 

 assemblage of coherent vegetable cells. Even the woody,/, and vascular, 

 c, d, e, tissues are produced by various modifications and functions of such 

 vegetable cells. As already mentioned, the thallogens are exclusively com- 

 posed of such cells ; and the very simplest forms of them, the lowest Algse, 

 consist but of a single cell, or are unicellular, Fig. 46, b. The ovule of the 

 highest plant, and the simple spore, are but different evolutions of this primi- 

 tive vegetable cell. 



Ultimately, therefore, all the vital functions performed by plants, viz., the 

 so-called vegetative functions, whether nutritive or reproductive, are accomplished 

 by the agency of cells. A vegetable cell, Fig. 46, c, consists of the following 

 parts : First, the cell-contents or endoplast a soft, usually colorless, fluid, slimy, 



