44 VEGETABLE ORGANS. 



made ; its structure resembles essentially that of the 

 plum-stone. In other instances the cells contain 

 secreted matters, as starch, oil, &c. ; and sometimes 

 the cotyledons also contain starch and oil. An ex- 

 ample of the former exists in the albumen of wheat ; 

 and of the latter, in the horse-chestnut, the filbert, 

 and mustard-seed. 



The albumen and cotyledons serve to supply the 

 embryo with nutriment until the roots have grown 

 sufficiently to enable them to absorb it from the soil ; 

 the cotyledons also serve as temporary leaves. 



The form and relative position of the radicle and 

 cotyledons serve to distinguish certain groups of 

 plants. This may be illustrated by the natural order 

 Cruciferse, or that containing the mustard, wall- 

 flower, &c. 



Thus, in one group, which may be represented by 

 the wall -flower, the cotyledons are flat or plane 

 (PL I. figs. 43 & 44), the radicle being applied to their 

 edges. This is best seen in a transverse section 

 (fig. 43). They are then called accum'bent (accumbo, 

 to lie against); and the botanical sign is 0=- In 

 the second group, the cotyledons are plane (PI. I. 

 fig. 38) , with the radicle applied to the back of one 

 of them, as in the seed of the common shepherd's 

 purse (Capsel'la bur'sa pastoris) (PL VII. fig. 19). They 

 are then termed iricumbent (incumbo, to lie upon), 

 and the sign is Oil. While in the third group the 

 cotyledons are folded in the middle, like the leaves 

 of a book (PL I. figs. 49 & 50), and the radicle is 

 enclosed between them, as in the white mustard 

 (Sina'pis alba) . The cotyledons are then called con- 

 duplicate (conduplico, to fold) ; and their sign is 0. 



The plants above-mentioned are evidently all Dico- 

 tyledonous, or their seeds have two cotyledons ; and 

 they contain no albumen. 



In the Monocotyledonous division, which may be 

 represented by a grain of wheat (PL I. fig. 53), the 



