Facts relating to the Structure of Seedlings. 267 
It is hardly necessary to point out that there is an obvious limitation 
to this expansion of bundles, so that in the seedlings of plants characterized 
by seeds of some size, it is usual to find several cotyledonary bundles 
the xylem of which may be more or less expanded. This necessity 
for, and realization of, several seed-leaf bundles is one of the factors which 
results in a large hypocotyl ; the other factors may next be considered. 
The above remarks apply chiefly to hypogeal seedlings ; in the case of 
seedlings with epigeal cotyledons, two features stand out prominently. If 
the seed leaves contain much reserve food material, e. g. the lupin, in addition 
to the problems relating to water supply and translocation of digested food 
there is the additional one of mechanics. A seed leaf replete with food must 
have a broad base of insertion on the hypocotyl, and the petioles, if present, 
must be stout structures ; also the hypocotyl, in order to bear the weight of 
the cotyledons, must be a fairly massive column. The mechanical require- 
ments of such massive structures are met, in part, by the development and 
proper disposition of several vascular bundles. 
But if the cotyledons do not contain much reserve food they, not 
infrequently in large seeds, early take on a photosynthetic function and 
exhibit a large surface; thus the same mechanical requirements may 
obtain, and also the desirability of an adequate supply of water. This 
is conveniently seen in the seedlings of Fagns sylvatica , a preliminary 
