W. Watson. 
149 
XEROPHYTIC ADAPTATIONS OF BRYOPHYTES 
IN RELATION TO HABITAT. 
By W. Watson, B.Sc. 
[With Three Figures in the Text.] 
I. Introduction. 
S OME years ago, when examining the bryophytesof the woodlands 
of Somersetshire (22), I was desirous of obtaining information 
on the characters which enable some species to live in dry situations, 
whilst others could only exist when provided with a large amount of 
shade or moisture. My search for information of this nature was 
only partially successful, as I could find no book or papers definitely 
dealing with it, but only scattered references to the subject in the 
works of Kerner (11), Goebel (7), Campbell (3), Haberlandt (9), 
Dixon (6), Warnstorf (19-21), Cavers (4, 5), Braithwaite (2), and 
others. Most of the required information had therefore to be gained 
from first-hand evidence by the study of the plants in the field and 
laboratory, and this paper is largely the result of such work, carried 
on for several years. A recent paper by Grebe (8) on the methods 
by which mosses protect themselves against drought, and an earlier 
series of articles by Wheldon (25), in which the xerophytic characters 
of some mosses were clearly shown and explained are of great value; 
these have been very useful to me in my later investigations, and 
extensively used in the arrangement of the matter for the present 
paper, which however deals with the liverworts as well as the mosses. 
Every investigator of the distribution of bryophytes is aware 
of the difficulty experienced in dealing with these plants, especially 
with some mosses, because of their entirely different appearances 
in the moist or dry conditions. In order that he may identify them 
in the field, the bryologist must know them in both conditions, for 
the same species may be so entirely different in these two states 
that he may easily believe himself to be dealing with two different 
species. The habitat must also be clearly noted by all collectors 
of bryophytes, so that the species may he quickly and accurately 
named, since a knowledge of the habitat in which the plant actually 
