AND BUXBAUMIA. 341 



necessity for this complete dispersion in Mosses seems to be 

 inversely as the size of the seeds. For in those genera of 

 the order in which the capsule either bursts irregularly or 

 has a naked mouth, the seeds are in general larger than in 

 those with a single, and still more manifestly than in those 

 with a double, peristomium. And in conformity with this 

 also, in Polytriclmm undulatum and lavigatum the tympanum 

 is sooner ruptured or removed thau in the other species of 

 the genus. 



The result of this comparison of Pohjtrichum with Lyellia 

 and Bawsonia, although it confirms the propriety of their 

 approximation, does not afford any clearly distinguishing 

 mark for the very natural section of the order which these 

 three genera form. In the mean time, however, it may be 

 circumscribed, though not with absolute precision, by a com- 

 bination of the more general characters which have been now 

 enumerated. 



LEPTOSTOMUM. 



In defining this genus, which was first proposed in my 

 former paper on Mosses^, I relied chiefly on the undivided 

 annular projection of the inner membrane of the capsule. I 

 was induced to employ this modification of the peristomium 

 as a character, though certainly far from being obvious, in 

 finding it to exist in several mosses of the southern hemi- 

 sphere, having a similar and peculiar habit : and which, had 

 it been neglected, I must have referred to Gyvinostomum, 

 with the greater number of whose species they have hardly 

 anything in common. 



Mr. Hooker, however, has since found, as he states, [673 

 the same structure in several other mosses, generally con- 

 sidered as having a naked peristomium, particularly in 

 Gymnostonmm microstonmm, Griffithianum, and fasciculare ; 

 and as these species have but little resemblance to each 

 other, and still less afiinity to Leptostomum, he has reduced 

 this genus also to Gymnostomum. 



If the statement referred to be correct, Leptostomum, 



1 [Fo/. 8,^. 352.] 



