12 ORGANOGEAPHY. 



Naxis developing in two opposite directions; the lower part is 



I called the descending axis or root {fig. 15, r), and the upper the 



I ascending axis or stem, t. Upon this axis or its divisions all the 



♦ future organs of the plant are arranged ; those which immedi- 



I ately succeed the cotyledons c c, constitute the true leaves of the 



, plant, dd; and all which succeed the leaves in the order of 



development, such as the flower and its parts, are merely 



modifications designed for special purposes of those organs 



which have preceded them. Hence the three organs, namely, 



stem, root, and leaves, which originally exist in the embryo 



in a rudimentary state, or are developed as soon as germina- 



Ition commences, are called the fundamental organs of the 

 'giant. They are also called organs j^~liMtr%iion or vegetation, 

 IsTecfause they have for their objectTthe nutrition and develop- 

 ment of the plant to which they belong ; while the flower and 

 its parts have assigned to them the of&ce of reproducing the 

 I plant by the formation of seeds, and are hence termed organs 

 I of reprodiiction. 



In like manner, when a spore germinates, it either simply 

 developes parts which perform equally both nutritive and re- 

 productive functions ; or a certain special apparatus is designed 

 for the latter purpose, as is the case in all the higher Cryptoga- 

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

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

 nutrition, and another for reproduction. Hence in treating of the 

 different organs of the plant, both in reference to their struc- 

 ture and functions, we arrange them into two divisions : namely, 

 1. Organs of Nutrition or Vegetation, and 2. Organs of Bepro- 

 duction. 



Having now given a general sketch of plants in different 

 degrees of organization, and of the compound organs which 

 they respectively present, we proceed to describe in detail the 

 elementary structures or building materials of which they are 

 composed. 



