58 ON SEEDLINGS 



100) ; in Cordia they are thrown into plaits (fig. 70). In. 

 others we have still more complex folds, as in the Beech. 



In such cases as the Lupine the cotyledons become so 

 fleshy and thickened that they almost lose the appearance of 

 leaves ; in this instance they are set free by the splitting of 

 the testa. When, however, the testa does not readily split, 

 and where in large seeds there is no endosperm, the difficulty 

 of unfolding the cotyledons and extricating them from the 

 seed becomes greater, and we arrive at cases where Nature 

 seems to have abandoned the attempt, and, as in the Oak and 

 Horse Chestnut, the cotyledons never quit the seed. Thus, 

 among the Juglandese, Pterocarya has leaf-like cotyledons, 

 while those of the Walnut never quit the shell. Every one, 

 however, must have observed the elaborate folds into which 

 the two cotyledons are thrown folds which seem to have no 

 significance or importance now, and which carry us back to a 

 time when the Walnut, like the Pterocarya, had foliaceous 

 cotyledons. 



If these suggestions be correct, we should expect that 

 species with non-emerging cotyledons would generally have 

 large seeds and be exalbuminous. This certainly appears to 

 be the rule ; among the species with reference to which I have 

 notes, there are 37 genera in which the cotyledons are sub- 

 terranean or remain in the seed. The seeds themselves are 

 notably large, and all but three are exalbuminous. Occasion- 

 ally we meet with subterranean and foliaceous cotyledons in the 

 same genus, as, for instance, in Ehus, Ehamnus, Mercurialis, 1 

 Phaseolus, &c. 



Phaseolus vulgaris presents us with an intermediate stage, 

 the cotyledons being aerial and green, but fleshy and by no 

 means true leaves. In Melittis melissophyllum, again, accord- 

 ing to Irmisch, 2 the fleshy cotyledons generally remain in the 

 seed, and are held together by the testa : but they sometimes 

 burst the shell, and stand out from one another. Like true 

 subterranean cotyledons, they have no stomata. 



When the cotyledons are large, thick, and fleshy they 

 often contain sufficient nourishment to render the plants for 



1 Winkler, Flora, 1880, p. 339. 



2 ' Zur Naturgeschichte von Melittis Melissophyllum,' Bot. Zeit. 1858, p. 233. 



