14 MB. W. MITTEN — BEYOLOGIA OF THE SXJBVEY 



two-nerved, and strongly one-nerved in the ultimate ramuli. 

 Notwithstanding, however, the difficulty of defining the distinc- 

 tions between the groups of Hypnoid mosses, Bridel's original 

 group Stereodon, although incompletely viewed by him, may be 

 said to differ from the Hypna of his arrangement in the more 

 cylindric, less indurated capsule and short operculum, and in the 

 habit of the species being somewhat different, the apices of 

 the stems not usually descending and rooting in a proliferous 

 manner as is the case with the Hypna. The mode of growth 

 of the greater number of mosses is very little understood; for 

 the comparison of a number of plants of the more abundant 

 species, such as Hypnum rutabulum, Linn., will show that the 

 habit assigned to Bhynchostegium, JSurynchium, and Scleropodiwm 

 of Schimper is found in that species as well, and that the stem 

 may be rooting its whole length, or erect and arcuate, or even 

 sub dendroid ; and as all are equally fertile, one cannot be said to 

 be less perfect than another. In the group Stereodon a number 

 of aquatic species become erect in their mode of growth, from, as 

 it would appear, their inability to increase in any other direction 

 from the crowding of the stems together. In the ' Musci 

 Indici ' there was confused with the section Stereodon all that 

 extensive group of species, chiefly tropical, which have distinct 

 alar cells, generally three more distinctly conspicuous in each 

 angle of the leaf, and a rostrate operculum; and these form 

 another section or genus, Sematophyllum, which passes through a 

 number of forms analogous to those of Hypnum and Stereodon. 



In all arrangements of the Order Musci, up to the latest in 

 M. Schimper's Synopsis (1860), the peristome is taken as the 

 chief distinguishing character, and genera have been founded, and 

 are maintained, upon characters dependent upon differences of 

 which the value has been greatly overestimated ; and even the 

 straightness or curvature of the capsule is considered sufficient to 

 constitute a distinct genus, and thus species are removed from 

 proximity to those to which in every other particular they are 

 so intimately allied as to be, in several cases, almost undistin- 

 guishable. Prominent examples of this occur in the Tricho- 

 stoma as here understood, in which there is a regularly ascending 

 series from Pottia through Anacalypta into Desmatodon ; and as 

 all these stages of development do occasionally occur in specimens 

 of the same species, the conclusion seems unavoidable that the 

 definition of a single genus should be sufficiently wide to con- 

 tain them all. Very nearly the same position is occupied by the 



