312 VEGETABLE ORGANOGRAPHY. 



developed upon the surface of each of these systems 

 which is in contact with the other system. To the first 

 the name of Endogens is given, to the latter that of 

 Exogens. The structure of the root of each class is 

 similar to that of the stem (Book ii. Ch. 1, 2). 



16th. The stem of vascular plants is furnished late- 

 rall} r with appendicular organs, which seem formed by 

 the expansion of one or more fibres (Book ii. Ch. 3). 



17th. These appendicular organs, although very dif- 

 ferent from one another in their appearances and uses, 

 seem however entirely identical in their original nature 

 (Bookiii. Ch. 2, sec. 18). 



Those which are already formed in the embryo, bear 

 the name of Cotyledons, or Seed-leaves; those 

 which are produced immediately afterwards, Primordial 

 Leaves. The following bear simply the name of 

 Leaves. Those which immediately surround the flower 

 receive the name of Bracts, and the flower itself is 

 composed of several verticils of appendicular organs, 

 much modified (Book ii. Ch. 3; Book iii. Ch. 1, 2). 



18th. The appendicular organs perform, according to 

 their position and mode of development, several different 

 functions, of which the principal are : — 



1st, That of nourishing organs, as the cotyledons and 

 leaves ; 



2d, That of protecting organs, as the scales of buds, 

 bracts, sepals, petals, carpels in their last stage ; 



3d, That of fructifying organs, as the stamens, and 

 the carpels during the first stage of their existence. 

 Several partake of both of these functions (Book ii. 

 Ch. 3; Bookiii. Ch. 1,2, 3). 



19th. The nourishing appendicular organs are, at 

 their origin, alternate in endogenous plants, called also 

 for this reason Monocotyledons ; opposite or verticil- 

 late in Exogens, called also Dicotyledons. In the 



