37^ 



MUSCINEJE, 



branches of each tuft turn outwards and upwards. The leaves spring from the stem and 

 the branches from a broad base, and are usually arranged with a divergence of ^; they are 

 tongue-shaped or apiculate, and, with the exception of the first on the young stem, are 

 composed of two kinds of cells arranged regularly. The young leaf necessarily consists 

 of homogenous tissue; but as the development progresses the cells of the veinless lamina 

 become differentiated into large broad cells about the shape of a long lozenge, and 

 into narrow tubular cells, running between the former, bounding them, and connected 

 with one another into a network ; they are, as it were, squeezed in among the larger 

 ones. The larger cells lose the whole of their contents, and hence appear colourless; 

 their walls show irregular narrow spiral bands with the turns some distance apart, as well 

 as large dots, each of which has a thickened edge, while the part of the cell- wall which 

 closes the dot is absorbed. Large, usually circular holes, are thus formed in the cell-wall 

 of the colourless cells. The intermediate tubular narrow cells retain their contents, 



;,r.S»>*^ 



Fig. ■2(>\.—SJ>hagnuni acniifoliunt ; A a portion of the surface of 

 the leaf seen from above, cl the tubular cells containing chlorophyll, 

 /"the spiral bands, / the holes in the large empty cells ; B transverse 

 section of a leaf, cl the cells that contain chlorophyll. Is the large 

 empty cells. 





Fig. ofi'i.— Sphagnum acntifoliutn ; A a male 

 branch, with the leaves partially removed in order 

 to shovK the antheridia a; Ban open antheridium 

 (very highly magnified) ; C a free motile anthero- 

 zoid (after Schimper). 



form chlorophyll-granules, and thus constitute the functional tissue of the leaf, the 

 entire area of which is, however, smaller than that of the colourless tissue (Fig. 261). 

 The stems consist of three layers of tissue, the innermost of which is an axial cylinder of 

 thin-walled, colourless, elongated, 'parenchymatous cells ; it is enveloped by a layer of 

 thick-walled, dotted, firm (lignified ?), prosenchymatous cells, with their walls coloured 

 brown. The epidermal tissue of the stem, finally, consists of from i to 4 layers of very 

 broad thin-walled empty cells, which, in S. cymbifolium, possess spiral thickenings and 

 round holes similar to those of the leaves {cf. Fig. 81). These colourless cells, both those 

 of the leaves and of the epidermal layer of the stem and of the branches, serve as a 

 capillary apparatus for the plant, through which the water of the bogs in which it grows 

 is raised up and carried to the upper parts ; hence it results that the Sphagna^ which 

 always grow erect, are penetrated with water to their very summits like a sponge, even 

 when their tufts stand high above the surface of the water. 



