2CX2 
STRUCTURE AND LIFE HISTORIES 
sporophytes of the ancestors of Sphagnum possessed true 
stomata and the function of photosynthesis. 
185. Formation of Spores. As the spore-case develops, 
the inner cells become differentiated into two kinds, one 
composing the larger part of the tissue, and the other, 
larger and richer in protoplasm, forming a dome of sporo- 
genous or spore-forming tissue 
near the upper wall (Fig. 145). 
From this tissue, spore- 
mother-cells are developed, 
and from each of these, by 
reducing divisions, as in the 
fern, four spores. 
186. Asexual Reproduc- 
tion. While the spores are 
maturing, a circular groove 
(annulus) is formed near the 
apex of the spore-case, and 
the cells in this zone have 
thinner walls than those ad- 
jacent (Fig. 145). At the 
maturity of the spore-case these cells become dry, and are 
easily torn apart, thus forming a lid, or operculum, at the 
summit of the spore-case. The falling away of the 
operculum affords an opportunity for the scattering of the 
spores. Under favorable conditions the spores germinate, 
putting forth a very short, green protonema, as in the case 
of fern-spores. The tip of the protonema soon broadens 
out, forming a prothallus, much like that of the fern in 
shape, but being only one cell thick (Fig. 146). Rhizoids 
form on the under side, and from the margin other 
threads develop, having chlorophyll, and resembling the 
FIG. 146. Sphagnumsp. A,B, 
young protonemata; C, older pro- 
tonema with leafy bud, k; r, mar- 
ginal rhizoids. (After Campbell.) 
