Page:An introduction to physiological and systematical botany (1st edition).djvu/393

 Rh hairy seeds; but the same circumstance will not justify us in separating a few species from Convolvulus, which are attached to that genus by stronger ties of another kind.

Some genera are obvious and indubitable both in habit and character, as Quercus, Rosa, Euphorbia, Begonia, ''Exot. Bot. t. 101, and Sarracenia, t. 53; others are obvious, but their character extremely difficult to define, 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 excellent 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 inextricable, a regular examination on scientific principles has led to the discovery of very natural well-defined genera. See Annals of Botany, v. 1. 501. I have in a preceding chapter hinted that the umbelliferous plants