192 STRUCTURAL BOTANY 



occupied by the embryo, is filled by a mass of 

 endosperm (see Fig. 91). Its cells contain reserve 

 starch and proteids, and have very thick cell-walls. 

 The whole tissue forms a great storehouse of food, 

 from which the young plant can draw supplies during 

 germination, before it is ready to shift for itself. 

 This is the most striking difference between the seeds 

 of the Lily and of the Wallflower : in the latter the 

 greater part of the endosperm is a transitory and 

 unimportant structure, which is used up long before 

 the seed is ripe ; in the Lily it forms a massive tissue 

 constituting the bulk of the ripe seed, and is only 

 consumed during germination. The Lily thus has a 

 typically albuminous seed, while the Wallflower is 

 nearly, though not quite, exalbuminous. As regards 

 the presence or absence of endosperm in the ripe seed, 

 there is no constant difference between the two Classes. 

 While, as we have seen, a large number of Dicoty- 

 ledons have albuminous seeds, many Monocotyledons 

 are exalbuminous, as, for example, the Orchids and 

 the Water-plantains. From one of the latter (Alisma 

 Plantago) our Figs. 89 and 90 were taken. In both 

 Classes a majority of the members have albuminous 

 seeds, and in almost all there is at least a temporary 

 formation of endosperm. 



The albuminous seeds of some of the Monocotyledons 

 have great practical interest. In Wheat, Eye, and the 

 other grains, it is the endosperm of the seed from 

 which flour is prepared. In fact, when we eat bread, 

 we are converting to our own use the stores of food 

 which the Wheat or Eye plant had provided for the 

 benefit of its seedlings. 



