DIFFERENCES IN ALLIED SPECIES 27 



so that they cannot grow any wider. On the other hand, 

 while the fruit of Oestrum is not very unlike that of Solairam, 

 the seeds are very different in shape, being peltate, more or 

 less obovate, with the broad end towards the apex of the seed, 

 so that the cotyledons have room to widen themselves. 



Sometimes we meet with species having both narrow and 

 broad cotyledons, even in the same genus. For instance, 

 Coreopsis filifolia (fig. 6) has narrow, Coreopsis auriculata 

 broad, cotyledons. If, however, we examine the seeds we find 

 that those of C. filifolia are narrow or subcylindrical (fig. 58), 



FIG. 58. Coreopsis filifolia. A, achene, x 14. B, longitudinal section, x 14. 

 C, transverse section, x 14. D, embryo, x 14. 



while those of C. auriculata (fig. 59) are broadly obovate ; 

 and as in both cases the embryo fills the seed, this difference 

 sufficiently accounts for the dissimilarity in the cotyledons. 



The genus Galium is an interesting case. Here also we 

 find some species with narrow, some with broad, cotyledons ; 

 but the contrast seems to be due to a very different cause. 

 G. Aparine (fig. 91) has broad, G. saccharatum (fig. 24) 

 narrow, cotyledons. In G. saccharatum the fruit (fig. 60) 

 deeply lobed, two-celled, two-seeded, indehiscent, and densely 

 covered with tubercles. The seed is globose, deeply hollowed 



