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 SpJiagnum are known, of 

 which about one-third are tropical ; but they are most abundant 

 in the north and south temperate zones, in the higher latitudes 

 of which they cover a large expanse of surface. 



Among the exotic species we may mention S. sericeum, 

 C. Mull., S. Holleanum, S. Junghuhnii, and .S\ Gedeanum, Dozy 

 et Molk., 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 kS". erythrocalyx, perichcetiale 

 subrigidum, sparsum, and gracilescens of Hampe, Caldense and pul- 

 chricoma, C. Mull. ; and in Central America we find S. Negrense, 

 limbatum, Mexicanum, and Peruvianum of Mitten, Meridense, 

 C. Mull., longifolium, Mandon, subcuspidatum, Schimp. From 

 Guadaloupe, 6". Antillarum, C. Mull., Guadalupense, Herminieri, 

 and Htisnoti, Schimp. ; and from Australia and New Zealand, 

 S. Mossmanni and cymbifolioides of C. Mull., Australe, molli- 

 culum, antarcticum, confertum, and Novo-Zealandicum of Mitten. 

 The only species from Tropical Africa is 6". Africanum, Duby. 

 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 Sphagna we find 

 a tendency to vary in two directions ; the first and most marked 



