116 EVOLUTION OF PLANTS 
They occur in almost all situations except in salt water 
and actual deserts, some being submersed aquatics, 
others growing upon the ground, or upon rocks and 
trees, and indeed in any situation where they can occa- 
sionally obtain moisture. Many of them may be com- 
pletely dried up for an indefinite period without losing 
their vitality. 
In the growth of the stem and leaves, as well as in the 
structure of the reproductive organs, the gametophyte 
is very uniform. Both leaves and stem show a definite 
apical growth, and the leaves are, with few exceptions, 
arranged spirally about the stem. The sexual organs 
are in the main like those of the Hepatice, but show a 
definite apical growth in both archegonium and anther- 
idium. 
The sporophyte is highly specialized and shows a 
certain degree of independence in the development of a 
well-marked assimilative system of tissues, as in Antho- 
ceros and Sphagnum. It differs in its growth from that 
of the liverworts in the presence of a definite single 
apical cell, to whose regular divisions the early growth 
of the embryo is due. Later this apical growth is re- 
placed by a basal growth much as in Anthoceros. 
The young sporophyte is a cylindrical body which 
later develops an enlarged upper portion, the capsule or 
theca, borne upon a long stalk, or seta (Fig. 29, D, sp). 
The latter is usually traversed by a strand of conduct- 
ing tissue, possibly homologous with the columella in 
the sporophyte of Anthoceros, or the vascular bundles 
in the young fern-sporophyte. 
The assimilative tissue in the sporophyte of the higher 
Musci is very perfect. The basal part of the capsule 
