766 LECTURE XLII. 



Stronger, but even it is devoid of the radicle, and probably also of the first leaves. It 

 is evidently not parasitism per se which induces this phenomenon, but chiefly the 

 want of chlorophyll; since the embryo of the Mistleto and other Loranthacese 

 abounding in chlorophyll attains not only a considerable size but is also provided 

 with cotyledons and radicle. 



It has already been remarked that in all seed-plants the seed containing the 

 embryo is simply the further developed ovule : the ovule in its turn, however, is as 

 we saw a macrosporangium, and the embryo-sac a macrospore, in which, after 

 fertilisation, the young plant — the embryo — has been developed from the oospore. 

 We might therefore designate the ripe seed still as a macrosporangium; but in 

 most instances this would not quite meet the case, for in the great majority of 

 Angiosperms the growing embryo-sac squashes the tissue of the nuceUus of the ovule 

 (i. e. of the sporangium) before or after fertilisation, so that it is finally surrounded 

 only by the integuments. From these, or from certain cell-layers of them, is 

 gradually formed the testa, the structure of which may be very different in the 

 various species. 



