( 55 ) 



TV.— On Bog Mosses. By E. Braithwaite, M.D., F.L.S. 

 Part III. 



Monograph of the European Species. 



Plate IX. 



About 55 species of Sphagnum are scattered throughout the world 

 nearly all of which have so much in common in their appearance 

 and habit, that we do not readily observe the characters requisite to 

 estabhsh good sjDecies and again to form these into sections. 



The structure of the cortical layers of the stem, and the form of 

 the leaves found on the stem, the fruit-peduncle and the divergent 

 branches, combined with the cell-texture of the same, afford the 

 characters on which we must principally rely for specific distinc- 

 tions, though the last named does not appear to be so invariable as 

 has been supposed, for the spiral threads contained in the cells 

 may partially disappear under certain conditions of growth. 



In the arrangement of the species Bridel adopts two sections, 

 Obtusifolia and Acutifolia ; and this plan is followed by Wilson in 

 the 'Bryologia Britannica.' 



C. Miiller, in his ' Synopsis Muscorum,' has a. with rounded 

 leaves, h. with truncate leaves, and the latter is again divided into 

 two, according as the peduncular leaves have or have not spiral 

 fibres. 



SuUivant, in Asa Grray's 'Botany of the Northern United 

 States,' arranges the species by the relative positions of the two 

 kinds of cells, seen on cross-section of a leaf, a character far too 

 minute, and difficult to be observed, to be of practical utility. 

 Prof. Schimper places all the species in two groups, Monoicous and 

 Dioicous ; also a most unpractical arrangement, as apart from the 

 inconspicuous nature of the flowers, the species are so frequently 

 found in a barren state, that such a mode of arranging them affords 

 no help to the student. Lastly Prof. Lindberg, in his paper 

 already quoted, which appeared in the ' Ofversigt K. Vetenskaps 

 Akad. Forhandlingar ' for 1862, has with a master's hand distri- 

 buted the Sphagna in natural groups, characterized essentially by 

 the form of the branch leaves, and leaving nothing to be desired. 



After separating S. macrojphyllmn as the genus Isodadus, 

 Prof. Lindberg divides the Sphagna into two sections, 1, Homo- 

 phylla having the stem leaves and branch leaves alike in form, 

 and destitute of threads. S. sericeum and 8. Holleanum from Java 

 and Sumatra belong here. 2, Heterophylla having the stem and 

 branch leaves of different forms, and in this section four groups 

 include the European species. In a letter recently received, my 

 kind friend alters the sequence of these, placing S. cymhifolium 



