SEED-COLORATION 393 



similarly responding to the young plant's needs, vigorous 

 growth begins. 



The lesson of the embryo of Poinciana regia will be dealt 

 with in Chapter XIX, where the general subject of the rest- 

 period of seeds is discussed. Brief reference will now be 

 made to the other two leguminous plants possessing the 



same seed-structure, namely, Cassia fistula and Bauhinia. They Cassia 



..,*,. . r i fistula and 



behave in a similar rashion as regards the coloration or the Bauhinia. 



embryo, which in the immature seed is bright green in the 

 first-named and pale green in the last-named plant ; but in 

 both cases it assumes a pale yellowish hue when the seed 

 enters upon the resting stage. 



The alteration in the colour of the embryo in seeds of Npn-legu- 

 the foregoing type, where the embryo with large foliaceous seeds, such 

 cotyledons lies between two slabs of albumen, sometimes 



amounts to complete decoloration as the seed proceeds with Cofubrina 



. asiatica. 



its development. Thus, in Hura crepitans (Euphorbiaceae) the 



embryo is coloured green only in the earlier stage of the 

 growth of the seed. When the seed has attained its full size 

 in the ripening fruit, and before the drying process has begun, 

 the embryo is already white, and that state it retains. It 

 would seem that the embryo in seeds of this type, whether 

 it be white or yellowish in the resting seed, has usually 

 functioning green cotyledons in the unripe or pre- resting 

 seed. This seems to be true also of the seeds of Ricinus 

 community in which, although (as I found) the embryo of the 

 resting seed is always colourless, the cotyledons may be green 

 in the pre-resting stage (see PfefFer's Physiology of Plants^ i. 596). 

 It may be inferred again in the case of Colubrina asiatica 

 (Rhamnaceae), where resting seeds of the same structural type 

 have pale yellow embryos. 



Since in the leguminous embryo the hypocotyl is relatively The colour 

 insignificant, the cotyledons making up its mass, I have usually 

 spoken of green embryos rather than of embryos with green 

 cotyledons. It would seem, however, that in this family when green. 

 the cotyledons are green the caulicle or hypocotyl may be 



