ORGANS OF KUTRITION. 69 



7-00^ r; and the upper the ascending axis or stem, t Upon 

 this axis or its divisions all the future organs of the plant 

 are arranged ; those which immediately succeed the cotyle- 

 dons, c, constitute the true leaves of the plant, d; and all which 

 succeed the leaves in the order of development, such as the flower 

 and its parts, are merely modifications designed for special pur- 

 poses of those organs which have preceded them. Hence 

 the three organs, namely, stem, root, and leaves, which origin- 

 allj" exist in the embryo in a rudimentary state, or are developed 

 as soon as germination commences, are called the fundamental 

 organs of the plant. They are also called organs of vegetation 

 or nutrition, because they have for their object tlie nutrition 

 and development of the plant to which they belong; Avhile the 

 flower and its parts have assigned to tliem the office of repro- 

 ducing the plant by the formation of seeds, and are hence 

 termed organs of reproduction. 



Ill like manner, when a spore germinates, it eitlier simply 

 developes parts which perform equally both vegetative and re- 

 productive functions ; or a certain special apparatus is designed 

 for the latter purpose, as is the case in all the liigher Crypto- 

 gamous Plants. We have here, therefore, as in Phanerogamous 

 Plants, two manifestly distinct series of organs, one adapted for 

 vegetation, another for reproduction. Hence in treating of the 

 different organs of the plant, both in reference to their structure 

 and functions we divide them into two divisions: namely, 1. 

 Organs of Nutrition or Vegetation, and 2. Organs of Reproduction. 



CHAPTER 3. 



ORGANS OF NUTRITION OR VEGETATION. 



Section 1. The Stem or Ascending Axis. 



The stem may be defined as that part of the axis which at its 

 first development in the embryo takes an opposite direction to 

 the root, (hence it is termed the ascending axis), seeking the 

 light and air, and bearing on its surface leaves and other leafy 

 appendages. This definition will only strictly apply to a stem 

 at its earliest development, for in numerous instances, soon after 

 its appearance, instead of continuing to take an upward direc- 

 tion into tlie air, it will run along the ground, or even bury itself 

 beneath the surface of the earth, thus withdrawing itself from 

 the light and air and resembling a root, with which organ such 

 a stem is commonly confounded. In these cases the stem is 

 liowever at once distinguished fi-om a root by the presence of 

 modified leaves, each of which has the power of forming a leaf- 

 bud in its axil (that is, in the angle produced by the junction of 

 F 3 



