OP GENERA. 363 



hairy seeds ; but the same circumstance will 

 not justify us in separating a few species from 

 Convolvulus, which are attached to that ge- 

 nus by stronger ties of another kind. 



Some genera are obvious and indubitable 

 both in habit and character, as Quercns, 

 Rosa, Euphorbia, Begonia, Eiot. Bot. t. 101, 

 and Sarracenia, t. 53 ; others are obvious, 

 bitt their character extremely difficult to de- 

 fine, as Valeriana. The greatest difficulty 

 lies in distinguishing genera that belong to 

 such very natural orders as the Grasses 

 and Umbelliferous plants ; and the ablest 

 botanists differ about the best guides in these 

 two particular cases. Yet other orders, 

 equally natural, sometimes afford very ex- 

 cellent generic differences, as that to which 

 Rosa, Rubus, Fragaria, &c, belong ; and 

 even in the Papilionaceous plants with ten 

 distinct stamens, a tribe hitherto judged in- 

 extricable, a regular examination on scientific 

 principles has led to the discovery of very na- 

 tural well-defined genera. See Annals of 

 Botanij, v. 1. 501. I have in a preceding 

 chapter hinted that the umbelliferous plants 



