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 znd Bauhinia. They Cassia 

 behave in a similar fashion as regards the coloration of 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 Non-legu- 



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



cotyledons lies between two slabs of albumen, sometimes *re^taiBand 



amounts to complete decoloration as the seed proceeds with Colubrina 



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 



communis, 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 cotyl wKn' 



spoken of green embryos rather than of embryos with green JgJL™*^ 



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



the cotyledons are green the caulicle or hypocotyl may be 



