370 



PLANT STUDIES 



from the seed. Formerly it was called either cauUde or 

 radicle. In Dicotyledons the stem-tip between the coty- 

 ledons often organizes the rudiments of subsequent leaves, 

 forming a little bud which is called the plumule. 



Embryos differ much as to completeness of their devel- 

 opment within the seed. In some plants, especially those 

 which are parasitic or saprophytic, the embryo is merely a 

 small mass of cells, without any organization of root, stem, 

 or leaf. In many cases the embryo becomes highly devel- 

 oped, the endosperm being used up and the cotyledons 

 stuffed with food material, the plumule containing several 

 well-organized young leaves, and the embryo completely 

 filling the seed cavity. The common bean is a good illus- 

 tration of this last case, the whole seed within the integu- 

 ment consisting of the two large, fleshy cotyledons, between 

 which lie the hypocotyl and a plumule of several leaves. 



245. The seed. — As in Gymnosperms, while the processes 

 above described are taking place within the ovule, the in- 

 tegument or integuments are becoming transformed into 

 the testa (Fig. 330). When this hard coat is fully devel- 



FiG. 330. The two figures to the left are seeds of violet, one showing the black, hard 

 testa, the other being sectioned and showing testa, endosperm, and imbedded 

 embryo ; the figure to the right is a section of a pepper fruit (Piper), showing 

 modified ovary wall (pc), seed testa (sc), nucellus tissue {p), endosperm (en), and 

 embryo (^m).— After Atkinson. 



oped, the activities within cease, and the whole structure 

 passes into that condition of suspended animation which is 

 so little understood, and which may continue for a long 

 time. 



