206 MOSSES. 



CHAP. Hi 



tudinal ; in some it consists of one valve and in 

 others of two valves, which at the period of the 

 maturity of the seed burst or open, sometimes 

 towards the nerves and sometimes towards the mar- 

 gin ; but in plants of a similar habit uniformly in 

 a similar manner. The merit of the discovery is due 

 By Sir J. exclusively to Sir J. E. Smith, the learned president 

 of the Linnsean Society of London, who has found 

 it to be a most decisive criterion for the determining 

 of natural genera, and the only sure ground on 

 which the botanist can rely.* In his luminous and 

 masterly Essay on the Genera of Dorsiferous 

 Ferns, as also in his Flora Britannica, he ap- 

 plies to the integument in question the term in- 

 volucrum, which is no doubt equally appropriate 

 with indusium ; but as the former term is already 

 pre-occupied in the description of umbelliferous 

 plants, it cannot with propriety be introduced into 

 the description of Ferns. 



CHAPTER II. 



MOSSES. 



Their THE Mosses are a tribe of imperfect plants of a 



character. ".' r. 



small and diminutive size, consisting otten merely 

 of a root surmounted with a tuft of minute leaves ; 



* Smith's Tracts, p. 227- 



