14 ORGANS OF NUTRITION.—ROOT.—STEM. 
having assigned to them the office of reproducing the plant by 
the formation of seeds, are termed organs of reproduction. 
In like manner, a spore in the course of its growth either 
simply develops parts which, as we have seen, perform equally 
both nutritive and reproductive functions ; or a certain special 
apparatus is designed for the latter purpose, as is the case in by 
far the larger number of Cryptogams. We have here, there- 
fore, as in Phanerogams, two manifestly distinct series of 
organs, one adapted for nutrition, and another for reproduction. 
Hence in treating of the different organs of plants, both in 
reference to their structure and functions, we arrange them in 
two divisions, namely: 1. Organs of Nutrition ; and 2. Organs of 
Reproduction. But before proceeding to describe these in detail, 
it is necessary that we should briefly define them, and explain 
the terms used in describing their principal modifications. 
1. Orcans or Nurrition. a. The Root.—The root (fig. 20, 
r)is that part of a plant which at its first development in the 
embryo takes a downward direction, 
Fie. 20. and is hence called the descending axis, 
avoiding the light and air, and fixing 
the plant to the earth or to the sub- 
stance upon which it grows ; or it is sus- 
pended in the water when the plant is 
placed upon the surface of, or in, that 
medium. The divisions of aroot, which 
are given off irregularly and without any 
symmetrical arrangement, are termed 
branches (jig. 20, r). 
b. The Stem or Caulome.—The stem 
(fig. 20, t) is that organ which at its 
first development passes upwards, and 
is hence termed the ascending axis, 
seeking the light and air, and bearing 
on its surface leaves, f, f, and other 
leafy appendages. The leaves are always 
developed at regular points upon the 
Fg er toa: surface of the stem, which are called 
mon Stock. 7. The root modes, and in the axil of every leaf (that 
es oa he is, in the angle produced by the junction 
Leaf-buds. ’"" of the base of the upper surface of the 
leaf with the stem) we find, under 
ordinary circumstances, a little conical body called a leaf-bud 
(figs. 20, b, b, and 22, b). From these leaf-buds the branches 
are subsequently produced, and hence, in the stem, these are 
symmetrically arranged, and not irregularly, as in the root, 
where there is no such special provision for their formation. 
It is in the presence of leaves and leaf-buds that we find the 
essential characteristics of a stem, as both these organs are 
absent in the root. 
