14. MR. W, MITTEN—BRYOLOGIA OF THE SURVEY - 
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 
cylindrie, 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 Rhynchostegium, Eurynchium, and Scleropodium 
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. 
subdendroid ; 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 tropieal, 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. Sehimper'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 
