Watson .— Sphagna: Habitats , Adaptations , and Associates. 541 
fine channels along which water passes by capillary action. In most species 
there are two or three divergent and one or two pendent branches (Fig. 2, B). 
In the two allied plants S. "cuspidatum and .S. recurvum , the former is 
a plant with a more characteristic aquatic environment, and this is reflected 
in the almost complete absence of pendent branches, especially in the wholly- 
immersed variety phimosum (Fig. 4, A), whilst the stem of recurvum is 
concealed by them, two or three of the four or five fascicled branches being 
pendent (Fig. 5, A). S. squarrosum , which, as its name implies, has 
squarrose leaves, often grows in shaded places, but when growing in open 
places has, like S. recurvum , two or three pendent branches which enable 
water to be drawn up from the constantly moist substratum. In the usually 
immersed S. riparium the pendent branches are scarce or absent, and in 
S. obesum , the most aquatic member of the Subsecunda group, they are 
wanting. 
The intermixture in the branch-leaf of empty hyaline cells with those 
containing protoplasm and chlorophyll is a generic character. The hyaline 
cells are provided with small openings or pores, strengthening fibres prevent 
collapse, and generally they are much wider than the alternating chloro- 
phyllous cells. They are regarded as water-reservoirs with a special 
aptitude for obtaining a quick and copious supply of water, and there is no 
reason to doubt this explanation of their presence, but the relative orienta¬ 
tion of the two kinds of cells, though constant for a particular species, is 
variable in the genus, and in some cases is suggestive of a protective device 
against undue loss of water from the living cells. It is also significant that 
in some submerged species, varieties, and forms, the hyaline cells are reduced 
or are replaced by chlorophyllous ones. In the submerged species, 5 . obesinn 
and .S. riparium , many of the cells, which are structurally hyaline, contain 
chlorophyll, and in a submerged form of S. imbrica'tum (form degenerans) 
the chlorophyllous cells are so much broadened that the hyaline cells 
sometimes seem to be absent. 
Fig. 3. Sphagnum subnitens. A. Portion of transverse section of stem, x 100. B. Surface 
view of two of the external cells of the stem, x ioo. c. Perichaetial leaf, x 16. D. Perichaetial 
leaf indicating the border of narrow cells, X 16. In the middle of the leaf the hyaline and chloro¬ 
phyllous cells are distinct; in the lower part they are indistinctly differentiated ; in the upper part the 
cells are smaller, relatively broader, and not differentiated. The hyaline cells have no fibres or pores 
and are one—or more—septate. F. Branch, bearing antheridia in the middle portion, x io. g. Leaf 
and antheridium, x 32. m. Three spores, x 400. The upper shows the papillose surface, the two 
lower show the triradiate marks. 
S. rubellum. E. Branch-leaf, x 30. 
S. inundatum. H. Stem-leaf with auricles, x 30. I. A few cells from the auricles showing 
incomplete or weak fibres, x 200. 
S. rufescens. j. Transverse section of stem, x 100. 
S’, subsecundum. K. Branch-leaf, x 30. o. Section of branch-leaf, x 400, showing two hyaline 
and two chlorophyllous cells. 
S. cymbifolium. N. Surface view of two of the outer cells of the stem showing fibres and pores, 
X 400. 
S, papillosum, p. Transverse section of branch-leaf, x 400. The outer surface is uppermost in 
the figure. 
All the leaves are figured as viewed from the inner surface. 
N n 2 
