THE BRYOPHYTES 425 
the formation of the sexual organs at the end of an axis of a 
shoot. They are either monecious, when both kinds of sexual 
organs are borne on the same plant, or diwcious, in which case 
the antheridia and archegonia arise on different plants. 
OrpvER 1.—SPHAGNALES, or Bog Mosses, including one 
family, Sphagnacee with the single genus, Sphagnum which has 
many species. Pale mosses of swampy 
habit whose gametophytes grow 
indefinitely at the apices of the stems 
repeating their growth periodically 
while their lower portions die away 
gradually and form peat, hence their 
frequent name of Peat Mosses. Peat 
in a dry state is used as fuel. The 
peat mosses possess a protonema 
which differs from that of other mosses 
in being thallose and bearing a resem- 
blance to the prothallus of a fern. 
The leafy stem ends in a three-angled 
apical cell and bears a branch at every 
fourth leaf. The branches divide to fy 
form secondary branches. The an- } 
theridia arise on small lateral branches 
in the leaf axils, each one consisting of 
a slender stalk and a globular capsule. 
The archegonia arise on the leafy tips of 
stems. The zygote gives rise to the 
Fic. 316.—Surface view of 
portion of a leaf of Sphagnum 
palustre showing reservoir cell (r); 
Sporophyte which possesses a large foot, transverse bands that prevent 
a small stalk and a spherical sporan- cells from collapsing (h); pores 
in reservoir cells (p); and green 
gium the end of which splits offasa 4. Sauuiaiae chiceopayil ()- 
lid to allow the spores to escape. 
A number of species of Sphagnum have been employed in 
surgery as absorbents in place of gauze. For this purpose they 
must be thoroughly cleaned and sterilized. 
The power which bog mosses have to absorb water depends 
on the presence of large chlorophyll-less cells the walls of 
which have pores and are supported by spiral or ring-like 
thickenings. These cells absorb water by capillarity. Between 
