8 THE SPHAGNACE OR PEAT-MOSSES OF 
pressure, as the form and direction of the branches and leaves 
can thus be better seen. 
Between fifty and sixty species of Sphagnum are known, of 
which about one-third are tropical; but they are most abundant 
in the north and south temperate zones, in the ae latitudes 
of which they cover a large expanse of surface. 
Among the exotic species we may mention S. sericeum, 
C. Mutt., S. Holleanum, S. Funghuhnu, and S. Gedeanum, Dozy 
et Motk., peculiar to the Eastern Archipelago, the two former only 
known in a barren state, but remarkable in having the stem leaves 
precisely like the branch leaves in form and structure, their hyaline 
cells being without fibres, but with a single apical pore. 
Brazil is rich in forms, comprising S. evythrocalyx, perichetiale 
subrigidum, sparsum, and gracilescens of Hampx, Caldense and pul- 
chricoma, C. Mii. ; and in Central America we find S. Negrense, 
limbatum, Mexicanum, and Peruvianum of Mitten, Meridense, 
C. MUL., longifolium, Manvon, subcuspidatum, Scuimp. From 
Guadaloupe, S. Antllarum, C. MUL.., Guadalupense, Herminieri, 
and: Husnoti, Scuimp.; and from Australia and New Zealand, 
S. Mossmanni and cymbifolioides of C. MULL., Australe, molli- 
culum, antarcticum, confertum, and Novo-Zealandicum of MitTTEN. 
The only species from Tropical Africa is S. Africanum, Dusy. 
It would be desirable that all the exotic species should be sub- 
mitted to a careful investigation and figured, although it would 
probably result in reducing their number, for each author appears 
to have set up a different standard in the characters regarded as 
specific. 
With respect to the great variability in some species of 
Sphagnum, it is difficult to decide on any determining cause: soil 
certainly does not appear to exert any controlling influence, for 
we may often see several varieties growing together in the same 
locality, but each preserving its proper character. The difference 
in the seasons, as regards moisture or drought, is probably an 
important factor in the question of development, size, or density ; 
but the colour must be the result of vital action, since it depends 
on the colour of the chlorophyl deposited in the narrow cells of 
the leaves, which, shining through the transparent hyaline cells 
while moist, gives the beautiful and varied tints to the Sphagnum 
tufts while growing in their native habitats, and so imperfectly 
retained in dried specimens. Probably in all Spagna we find 
a tendency to vary in two directions ; the first and most marked 
