VEGETABLE PHYSIOLOGY. 
123 
% 
3 
without much difference of form, and the greater firmness resulting from a closer packing of the 
component cells and a thickening of their walls by deposits, here usually of a tough, jelly-like, or 
horny consistence, produced in the same way as the harder secondary deposits of wood-cells. In the 
Fungi, the cells are usually very delicate and loosely packed, hence the soft and spongy character 
of these plants. The Lichens have the cells developed to a horny or papery consistence, giving them 
that dry and rigid character which is so peculiar to this tribe. The Algie, on the other hand, inhabi¬ 
tants of water, are soft and gelatinous in texture, acquiring greater substance and a grisly, or even 
somewhat horny nature, in those instances where they are exposed to violent external influences, as 
of the beating of water upon the rocks where they flourish. In all these plants the processes of 
nutrition are very simple, there is no distinction into leaf, stem, and root, and every part of the 
plant is equally capable of performing any of the functions belonging to the life of the plant. In 
the Algie, for instance, all the cells are engaged in the process of assimilation of the nutriment derived 
from the water in which they live ; each cell is at once its own root and leaf, absorbing the crude food, 
and converting it into organized matter. The Lichens live in the same way, on the moisture they 
absorb from the air ; and the Fungi in decomposing liquids or other decaying matters. The only kind 
of circulation we can imagine to exist here, is a distribution or equalization of the fluids throughout 
the textures, where, for instance, a part of the plant fully exposed to moisture conveys a portion of 
its absorbed fluid to a drier part, in a manner which may be roughly compared to the soaking of 
water along a piece of blotting-paper, or through a sponge or other porous body. 
Connected with this physiological independence of the cells in regard to nutrition, we usually find 
an equal independence of vitality, that is to say, the cells, thus combining all the nutrient functions 
in themselves, are capable of sustaining life and continuing their growth when separated by external 
violence from each other. But to this point I shall return hereafter. 
Advancing to a higher class of vegetables, we find in the Mosses very distinct signs of a more 
elevated organization. Here we first see a true distinction of parts which may be properly called leaf, 
stem, and root, and corresponding to the marked increased variety of components of the outward form, 
we find a new kind of structure in the interior; we now find the cellular tissue strengthened by a 
regularly arranged woody skeleton. The Mosses in general are almost wholly cellular, but in them 
we find the first traces of the fibrous formations which in their more highly developed condition con¬ 
stitute the wood and fibrous bundles of flowering plants. Thus the thread-like cellular stem of a 
Moss has a fibrous core, as it may be called, a little bundle of true woody tissue running up its centre, 
and in some instances sending off little branches to form mid-ribs to the leaves; these leaves are 
usually single layers of flattened plates of cellular tissue, closely resembling the leaf-like expansions 
found in some of the Algte, but sometimes these cells are strengthened by curious spiral deposits in 
the interior, as in the Sphagnum or Bog Moss. The roots are mere threads formed of several rows of 
very delicate cells, and these roots, which penetrate the soil, now exclusively exercise the office of col¬ 
lecting food for the plant, while the functions of digestion and respiration are removed to a separate 
seat in the leaves; ■ we now no longer see that uniformity or indifference of colouring in the different parts 
of the plant, the absorbing roots contain only colourless juices, while the leaves owe then tint to the pres¬ 
ence of abundance of that highly organized form of assimilated food, the chlorophyll granules or vesicles. 
The tribes standing between the Mosses and the flowering plants, namely the Club Mosses, the 
Ferns, and their allies, differ principally from the first in their greater complexity, but they also pre¬ 
sent us with the first examples of the spiral structures in the so-called vessels or ducts. The woody 
column running up the centre of the stem of a Lycopodium or Club Moss, for example, consists of a 
perfect “ fibro-vascular bundle,” that is to say, it is no longer a thread of simple elongated wood-cells, 
but is composed of a number of “ spiral vessels” (i. e. very long and slender cells with a spiral fibre 
coiled up in their interior) surrounded by a considerable collection of wood-cells. In the Ferns, where 
the stems acquire much greater size, growing even into trunks rivalling those of the Palms, we find 
the “skeleton” of the stem composed of a number of analogous “fibro-vascular” bundles, arranged in 
an irregular ring; and, in the older conditions of the arborescent kinds, these acquire great solidity of tex¬ 
ture. The subdivisions and branches of this skeleton, which run out to form the ribs and veins of the leaves, 
partake of the higher character of organization, and we find the veins of the leaves of Ferns, &c., 
to contain spiral structures similar to those of the bundles in the stem of which they are prolongations. 
In the flowering tribes we have to distinguish two great divisions, differing in almost every respect 
in their structure, and in no point more than in the anatomy of then’stems. 'These divisions are called 
the Monocotyledons and the Dicotyledons, from the condition of the embryo or germ contained in their 
seeds; they have also been called Endogens and Exogens, from a supposed contrast in the mode of 
growth of their stems, but the hypothesis oil which these names were grounded was the result of im- 
vyo 
