CHAPTER XXIII 

 THE SEED AND ITS GERMINATION 



WE have already seen (p. 363) that different seeds vary 

 very much in the size attained by the embryo when the 

 seed is ripe, apart from the dimensions of the seed 

 itself, which varies from the microscopic seeds of orchids 

 to the enormous seed of the coconut. During develop- 

 ment the embryo absorbs more or less of the endosperm, 

 but in some cases it is still surrounded by endosperm 

 in the ripe seed, while in others it absorbs the whole 

 of the endosperm and comes to occupy the entire space 

 within the testa. Seeds in which endosperm is still 

 present at maturity are called endospermic seeds, 1 

 and those which have no endosperm left when they 

 are ripe are non- endospermic* Examples of the former 

 are wheat, maize (and the cereals generally), castor 

 oil, date, etc. : of the latter, bean, pea, acorn, etc. In 

 non-endospermic seeds the embryo, and especially the 

 cotyledons, are often large and swollen, their cells packed 

 with the food material which in the endospermic seeds 

 would remain in the endosperm till the time of germina- 

 tion. This food material takes the forms with which 

 we have already become familiar. The nitrogenous 

 organic substance is in the form of solid grains of protein 

 material, the non-nitrogenous, either as carbohydrate 

 starch grains, or more rarely as thick cellulose walls 



1 The old name is " albuminous seeds," from the analogy of the 

 " white " or " albumen " of a bird's egg, which, like the endosperm, 

 is a store of food for the developing embryo. 



* Or " exalbuminous." 



375 



