THE BRYOLOGIST. 
Vol. XI. November, 1908. No. 6 
SOME RELATIONS BETWEEN THE HABITATS OF MOSSES AND 
THEIR STRUCTURE. 
A. J. Grout. 
Fifteen years of study of North American mosses both in the field and 
herbarium have convinced the writer that many peculiarities of moss struc- 
ture are a direct result of peculiarities of habitat. It is, of course, extremely 
difficult to determine whether in any given case a peculiarity in habitat cor- 
related with a peculiarity of structure, has a causal relation or is merely a 
coincidence. Besides it is difficult to find such relationships that are not more 
or less obscured by exceptions to the general run of facts. The present 
article is put forth as tentative and suggestive, yet it seems to the author that 
it certainly contains much of truth, possibly interwoven with more or less 
misinterpretation. 
There are numerous cases where mosses of widely different relationships 
but of a common habitat, possess strikingly similar characteristics. These 
similarities must often be due to similar conditions of life. The fact that this 
has not always been recognized has led to many classifications not at all 
natural, as for instance the Cleistocarpi. 
First let us consider the sporophyte. Here the most striking fact to 
me is that mosses growing largely or wholly on tree trunks have erect cap- 
sules. Here we have many species of Orthotrichaceae , Leucodontaceae , 
Fabroniaceae , Neckeraceae , Leskeac.eae and Hypnaceae. An examination 
of some cases of erect capsules in the Hypnaceae illustrates this relation most 
strikingly. Species classed with Homalothecium ( Euhomalothecium of 
Cardot) are not separable from Camptothecium except by sporophyte char- 
acters. In Brachythecium the erect-capsuled species, B. acuminatum 
(Hedw.) Kindb., B. cyrtophyllum Kindb. etc., are largely tree-growing. I 
believe it is not the substratum but the position of growth that causes this 
modification of the capsule so that we find a similar modification in species 
that grow largely on faces of cliffs or in fissures of cliffs, e. g. Brachythe- 
cium collinum and its allies. Pylaisia is certainly closely related to many 
species of Hypnum having curved capsules, and Amblystegium adnatum , 
largely a tree-growing species, has nearly erect capsules. Many more illus- 
trations could be given but the above will suffice. 
Let us consider in what way this growing on a more or less vertical sub. 
stratum could affect the structure of the capsule. It has undoubtedly been 
brought about through the medium of spore dispersal. We shall find that 
very few mosses with erect capsules have complete double peristomes, even 
if most closely related to others having typically developed double peristomes 
with segments and cilia, e, g. Pylaisia , Brachythecium acuminatum and 
Homalothecium. The Orthotrichaceae as a rule have only a trace of the 
inner peristome. 
The September BRYOLOGIST was issued September 1, 1908. 
