370 



PLANT STl'DIKS 



from the seed. Formerly it was culled either cuullrJe or 

 radicle. In Dicotj'ledons 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 jiarasitic or saprophytic, tlie embryo is merely a 

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

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

 ojicd, the endosperm being used up and the cotyledons 

 stutled with food material, the plumule containing several 

 well-organized young leaves, and the embi'yo 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- 



Fir.. .330. Tlii' two IIl'imts to tlio left are seeds (if viij|,-t, one showinf; tlie lila.'k, lianl 

 te-sta, tlie other lieiiiL' sectioned and phowitiLf testa, endosperm, and iniliedded 

 emtjryo : tin- Il^no'e to the right is a se<'tion of a pepper fruit iP/yk/i, show iiiLr 

 modified ri\'ary wall l/"l, seed testa (.sci, niicelhis tissue (/>), endosperm (-//I, and 

 embryo d-/// ).— A fter Atkinson. 



oped, the activities within cease, and the whole structure 

 passes into that coTidition of suspended animation which is 

 so little understood, tind which iiuiy continue for a long 

 time. 



