95 
to very different conclusions regarding them. Dawson Turner, 
in his ‘ Muscologia Hibernica, in 1804, enumerated only 3 
species. Bridel Brideri in his ‘ Bryologia Universa,; in 1827, 
raised the number of species to 7. Wilson, in the ‘ Bryologia 
Britannica, in 1855, gives 9 species divided into the sections 
obtusifolia and acutifolia. Schimper, in his ‘ Synopsis Muscorum 
EHuropeworum, 2nd ed., enumerates 20 species divided into 6 sec- 
tions; and Milde, in the ‘ Bryologia Silesiaca, (1869), has re- 
duced the number to 16 species, under 4 sections. Braithwaite, 
in the ‘ Sphagnacew Britannice exsiccate, gives 1'7 species and 
36 varieties, divided into 4 sections. 
All these, as well as many other systems that might be men- 
tioned, only show the difficulty of discovering any good simple 
natural system of arrangement, the need of which becomes more 
evident when we think of the number of varieties and forms in 
some of the species. For example, in S. acutifoliwm we find 11 
named varieties, and some of these varieties show a large num- 
ber of forms varying in an unbroken series from the most slender 
to the most compact, yet all maintaining the characters of the 
variety. But in addition to the great diversity observed in each 
species and variety, we see great resemblance between some of 
the varieties of distinct species, e.g., a squarrose variety occurs in 
several species besides S. sguarrosum, and the character is fully 
as well marked in some forms of S. compactum, S. cymbifoliwm, 
S. acutifolium, and (less frequently) S. molle and S. 2 reinwm, as 
in S. squarrosum itself. Notwithstanding these difficulties I 
think that in the annexed table the arrangement of them is so 
much simplified that the collector will be able to distinguish 
the species with the aid of a good pocket lens, as he gathers 
them. 
The sections are based entirely on the characters of the stem- 
leaves, and the minor divisions on easily observed characters in 
the plants generally. It may be objected that this is a reversion 
to an artificial system, and this may be in so far true as the 
groups are based on variations of a single organ, but yet the 
groups are natural enough, indeed fully as much so as in the so- 
called natural systems, and in the study of cryptogamic plants 
the simpler the plan of grouping the more natural is the result 
generally found to be. In Sphagna, for instance, the knowledge 
of the exact form of the cells, and of the exact form of the cell- 
walls is very interesting to those who have time and means to 
acquire it, but it is not necessary for the classification of the 
species, and should be dispensed with if more easily employed 
characters can be found sufficient for the purpose, and these are 
I think to be found in the stem-leaves as already mentioned. 
As regards the number of species, I believe it is of little im- 
