TYPES OF CRYPTOGAMS; BRYOPHYTES 281 
its allies consist chiefly of the thallus in the vegetative con- 
dition, while the greater number of Hepaticz have a stem 
and leaves. Thus they approach closely to the mosses. 
But mosses usually have leaves on all sides of the stem, 
while the leaves of Hepatic are two-ranked, spreading 
laterally, with sometimes a third row of leaves or scales 
underneath. ‘The leaves of mosses usually have more than 
one layer of cells in some part, but the leaves of the leafy 
Hepatice have but one layer of cells throughout. The 
forms of the leaves are often very curious and interesting. 
The sporophyte of most mosses consists of a capsule with 
a lid, while in the leafy Hepatice the capsule usually 
opens by splitting longitudinally into two to four valves. 
Different species of Hepatic grow on damp soil, rocks, 
and the bark of trees. Many are capable of enduring 
drought and reviving with moisture. 
THE STUDY OF PIGEON-WHEAT MOSS 
(POLYTRICHUM COMMUNE) 
343. Occurrence. — This moss is widely distributed over the sur- 
face of the earth, and some of its relatives are among the best 
known mosses of the northern United States. Here it grows 
commonly in dry pastures or on hillsides, not usually in densely 
shaded situations. 
344. Form, Size, and General Characters. — Study several speci- 
mens which have been pulled up with root-hairs. Note the size, 
general form, color, and texture of all the parts of the plants exam- 
ined. Some of them probably bear spore-capsules or sporophytes like 
those shown in Fig. 206, while others are without them. Sketch one 
plant of each kind, about natural size. 
What difference is noticeable between the appearance of the 
leaves in those plants which have spore-capsules and those which 
have none? Why is this? 
