Inquiry into the Structure of Seeds. 227 



sequence of the more intimate connection between it and 

 the latter than either or* ihem has with any other part, which 

 is also precisely true of the cotyledons and embryo, as above 

 mentioned. For these reasons T presume the vitellus to 

 differ in no respect from the subterraneous cotyledons al- 

 ready described ; and that its office is to perform the neces- 

 sary functions relative to air or oxygen, till the leaves come 

 forth and assume those functions, in greater -perfection, 

 with the cooperation of light. This seems more satisfactory 

 than the opinion of Gsertner, that the organ under consi- 

 deration affords nourishment to the embryo } because this 

 is abundantly supplied by the copious albumen of a multi- 

 tude of seeds whose vitellus is very inconsiderable, as grasses ,' 

 and because it is mi philosophical to recur to two causes, 

 when one is evidently sufficient. In fact, the vitellus, as far 

 as I can observe, only dwindles away when the leaves un- 

 fold, exactly as happens to the subterraneous cotyledons. 

 The same thing very often takes place as speedily in those 

 which rise out of the ground ; the existence of the latter ap- 

 pearing to be prolonged in some instances, merely by their 

 nearer approach to the nature of leaves, as in umbelliferous 

 and cruciform plants. The difference of duration is still 

 more evident, and more instructive as to our present pur- 

 pose, in the leguminous family, between such cotyledons as 

 rise above the ground, like lupines, and those wjiich remain 

 buried, like vetches, the latter decaying as quickly as any 

 supposed vitellus can do. In grasses the scale, taken by 

 Gaertner for a vitellus, is mostly so thin and unsubstantial, 

 as not possibly to contain any material portion of nourish- 

 ment ; but its expanded figure is very well calculated, like 

 that of the leaves, for functions analogous to vegetable respi- . 

 ration, and its whole aspect conveys the idea of a primary 

 or subterraneous leaf, quickly rendered superfluous by the 

 production of real leaves, which, as well as the radicle, are 

 probably, in the first stage of their evolution, fed by the 

 abundant juices of the albumen. It appears that the pre- 

 tended vitellus is not necessary to all plants furnished with 

 this distinct kind of albumen. The palms and orchidece 

 prove to be destitute of it. On the other hand, I can find 



P 2 no 



