DR. STIRTON’S BRITISH MOSSES 
11 
study all of them. In view of a forthcoming 3rd edition of the 
Student's Handbook of British Mosses it became necessary to 
ascertain the value of these; I have therefore made a careful investi¬ 
gation of the material in the collection, and it appears desirable to 
publish the results at which I have arrived. 
That out of this large number of species all but a very few will 
be found in the following revision to be reduced to the synonymy of 
one or other of our wellknown mosses may seem to demand some 
justification. It arises from two or three distinct causes—-primarily 
because Stirton’s conception of a species differed materially from that 
of most of our bryologists. This is, of course, a matter on which no 
two opinions will exactly coincide, and it may be held presumptuous 
for me to set my opinion against Stirton’s. But, after all, there is a 
fairly recognizable standard of “ common opinion ” to which test any 
personal view may be brought; and the maxim “ quod semper, quod 
ubique, quod ab omnibus, etc.” is applicable to scientific as well as to 
theological doctrine. It could easily be shown over and over again 
from his own descriptions, quite apart from any personal individual 
view, that what to Stirton constituted a specific character does not 
often amount to more than would, in the opinion of most bryologists, 
give at best the rank of a variety, usually of a form only. 
In the second place, Stirton relied to a considerable extent, parti- 
cularly in certain genera like Campy lop us, on minutiae of cell measure¬ 
ment which no other brvologists have found sufficiently constant or 
well defined to be of real value as constituting specific characters. 
And, in addition to these general considerations, there are naturally a 
certain number of his species which must be rejected because founded 
either on an error of observation, or by overlooking some affinity, 
such as falls to the lot of all scientific workers at one time or another. 
A more difficult problem is how far some of the species are entitled 
to the rank of varieties. Opinion there would probably differ more 
than on the question of specific rank. In the Student's Handbook I 
have restricted the number of varieties within very narrow limits, 
some would no doubt say too narrow. The hobby-horse of variety- 
making, when ridden with a loose rein, is apt to run away with its 
rider. And considerations of space have to be taken into account. 
1 have therefore only in a few cases retained Stirton s species in the 
rank of varieties, though freely admitting that it is open to question 
whether certain others may not deserve that rank. On the whole, 
however, the number of doubtful cases is really few; it will be seen 
that I have, in the case of quite a number of the species, identified them 
with varieties already existing. 
Moreover, many of the species, especially of Campylopus , are 
based purely or principally on colour, a quality which, I think, by 
itself is too superficial to be held of specific value, and only rarely 
should constitute varietal rank. Finally a certain number—especially 
of Campylopus —are based almost entirely on minute, quantitative 
differences of internal, histological structure. Now whether rightly 
or not, varietal differences as usually conceived, are for the most part 
concerned with external characters; and there would seem to be 
something incongruous, whatever be the histological value of the 
