378 MUSCINEm, 
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-w^all 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, 
Fig. 26i.~Sphac^num acutifoliutn ; A a portion of the surface of 
the leaf seen from above, cl the tubular cells containing chlorophyll, 
/"the spiral bands, I 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. 262. — Sphagnum acnti/olium ; A a male 
branch, with the leaves partially removed in order 
to show the antheridiaa:; Äan 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. 
