332 SPHAGNUM. JART n. 



genus, Sphagnum, which consists of some eight or ten 

 species and several varieties. The species of Sphag- 

 num, or common bog moss, hold an important place in 

 the economy of nature. They are floating mosses, 

 entirely destitute of roots. The stalk of the full grown 

 plant, like that of land mosses, is constructed of three 

 kinds of cells ; one forms the exterior or cortical layer, 

 another forms the central pith or axial system, while 

 the third, which is coloured and somewhat ligneous, 

 comes between the other two. The leaves, which have 

 their origin in the cortical layer while it is yet soft, 

 consist of two kinds of cells, one kind being large, elon- 

 gated, and colourless, and containing spiral fibres loosely 

 coiled in their interior. The membranous walls of 

 these cells have large round apertures by which their 

 cavities have free communication ; for certain animal- 

 cules, which sometimes live in the cells, have been seen 

 to pass from one to the other. Between these colour- 

 less cells are some thick-walled, narrow, elongated 

 green cells, which give the leaf firmness and colour. 

 According to Mr. Wilson, the fascicles, or bundles of 

 branches, are disposed round the stem in imbricated 

 spirals, so that, for every complete spiral formed by five 

 of these fascicles, there are eight spirals formed of 

 twenty leaves, four leaves being inserted between each 

 pair of fascicles. The fructification in all these float- 

 ing mosses is immersed in the leaves of the stem, the 

 antheridia being globose, and the spermatozoids having 

 spiral motions, both within the cells of the antheridia 

 and when they come out. The urns, which are the pro- 

 duct of fructification, and are borne at the top of what 

 appears to be a long footstalk, but is in reality a pe- 

 dunculate vaginula, are globular, and their lids have been 

 observed to be driven off when the spores are ripe, with 

 such force as to give a distinctly audible report. 



