48 ON SEEDLINGS 



In Seneeio, again, the majority of species have entire 

 cotyledons. In some, however, as in S. erucaefolius, they are 

 emarginate. Even here, however, they are at first entire 

 (fig. 93), and the emargination does not make its appearance 

 until after germination, when the cotyledons gradually become 

 much widened (fig. 94). In fact, S. squalidus, S. viscosus, 

 S. vulgaris, &c. have the cotyledons narrow and entire ; while 

 in S. erucaefolius and S. cruentus, where they grow more in 

 width than in length, they become emarginate. Among other 

 cases where the cotyledons are at first entire, but after ger- 

 mination become emarginate, may be mentioned some species 

 of Lithospermum. 



Bryonia laciniosa (fig. 75) also has the cotyledons emargi- 

 nate, while in B. dioica (fig. 76) they are entire. They are, 

 however, originally entire in both cases, and the emargi- 

 nation in B. laciniosa is due to the fact that in that species 



FIG. 93. Young seedling of FIG. 94. Ditto, a few days 



Seneeio eruc&foUus. older. 



the cotyledons grow much more than in B. dioica. There is 

 no great difference in size between the seeds, those of B. 

 laciniosa being perhaps one-tenth larger. On the other 

 hand, the cotyledons of B. laciniosa attain a length three times 

 greater than those of B. dioica, as shown in the figures (figs. 

 75 and 76). In the genus Tacsonia, again, the cotyledons are 

 entire in T. Van-Vokemi and T. Leschenaultii, and emarginate 

 in T. ignea. Here also, however, they are at first entire, and 

 only become emarginate after leaving the seed. 



DIVIDED COTYLEDONS. 



The genus Pterocarya has very curious cotyledons (fig. 41), 

 due to a cause entirely different from any of those we have 

 considered hitherto. 



They are bipartite, each primary division narrowing to a 



