210 



PLANT STKUCTURES 



ledons often organizes the rudiments of subsequent leaves, 

 forming a little bud which is called the plumule. 



Embryos differ much as to com- 

 pleteness of their development within 

 the seed. In some plants, especially 

 those which are parasitic or sapro- 

 phytic, the embryo is merely a small 

 mass of cells, without any organiza- 

 tion of root, stem, or leaf. In many 

 cases the embryo becomes highly de- 

 veloped, the endosperm being used 

 up and the cotyledons stuffed with 

 food material, the plumule contain- 

 ing several well - organized young 

 leaves, and the embryo completely 

 filling the seed cavity. The com- 

 mon bean is a good illustration of 

 this last case, the whole seed within 

 the integument consisting of the two 

 large, fleshy cotyledons, between 

 which lie the hypocotyl and a plu- 

 mule of several leaves. 



115. The seed. As in Gymno- 

 sperms, while the processes above 

 described are taking place within 

 the ovule, the integument or integu- 

 ments are becoming transformed into the testa (Fig. 183). 

 When this hard coat is fully developed, the activities 

 within cease, and the whole structure passes into that con- 

 dition of suspended animation which is so little under- 

 stood, and which may continue for a long time. 



The testa is variously developed in seeds, sometimes 

 being smooth and glistening, sometimes pitted, sometimes 

 rough with warts or ridges. Sometimes prominent append- 

 ages are produced which assist in seed-dispersal, as the 

 wings in Catalpa or Bignonia (Fig. 184), or the tufts of 



PIG. 182. Young embryo of 

 water plantain (Alisma), a 

 Monocotyledon, the root 

 being organized at one 

 end (next the suspensor), 

 the single cotyledon (C) 

 at the other, and the stem- 

 tip arising from a lateral 

 notch (v). After HAN- 

 STEIN. 



