570 Mr. Brown 07i Lyellia, Leptostomum, and Buxbaumia. 



I have observed, never form complete septa, at least in the ripe 

 fruit; though in those species having quadrangular capsules they 

 nearly reach the parietes opposite to the external angles, towards 

 which they are directed. 



As the columella of Polytrichum retains its regular form in the 

 ripe capsule, its real structure may even then be in a great measure 

 determined. In this stage I find its wings, or compressed sides, 

 to consist of a double membrane with an intermediate spongy 

 substance, in which there is no appearance of granules; and 

 the internal denser substance of the axis is equally free from 

 granular matter. But as there is no indication of lateral rup- 

 ture, the sides in several species remaining perfectly smooth, nor 

 of any central cavity, this structure affords a powerful argu- 

 ment in refutation of those hypotheses which assume the exist- 

 ence of two kinds of granules in the capsules of mosses ; the one 

 produced in the cavity formed by the internal membrane, the 

 other in the substance or supposed cavity of the columella itself; 

 the latter being considered as seeds in one of the hypotheses*, 

 and in the other as polIen-|-. 



This argument, however, is not here advanced to disprove the 

 existence of two kinds of granules in the capsules of mosses, but 

 merely against their production in the distinct cavities assigned 

 to them in the hypotheses referred to. 



In the greater number of Polytvicha as well as in Lyellia and 

 Dawsonia the seeds are extremely minute ; a fact with which the 

 increased surface for their production is probably connected : for 

 in P. undulatum, where the seeds are larger than in most other 

 species of the genus, this increased surface does not exist ; and in 

 P. Icsvigatum, where they are of still greater size, the plicae of the 

 inner membrane are probably also wanting. 



* Palisot Beauvois, ^thiog. p. 5. f Keith, Physiol, Bol. ii. p. 346. 



Although 



