290 EVOLUTION OF PLANTS 
from the fertilized egg-cell, is very simple in structure, 
and is devoted almost exclusively to spore-production, 
having no power of independent growth, but living as 
a parasite upon the tissues of the gametophyte. Within 
the Hepatice, however, are forms in which the sporo- 
phyte becomes much more important, and in the genus 
Anthoceros, especially, it reaches a large size and 
becomes almost independent of the gametophyte owing 
to the development of several layers of green tissue 
communicating with the atmosphere by means of sto- 
mata, exactly as in the higher plants. Here, too, only 
a small part of the tissue is devoted to spore-formation, 
and the growth of the sporophyte does not cease as soon 
as the first spores are ripe. No root, however, is de- 
veloped, and the sporophyte remains dependent upon 
the gametophyte for its supply of water and for such 
food elements as it cannot obtain from the air. The 
duration of its growth is therefore determined by 
that of the gametophyte. 
The gametophyte in the Bryophytes may reach a very 
considerable size, and is sometimes quite complicated 
in its structure, but this does not necessarily corre- 
spond to the development of the sporophyte, which 
reaches its highest expression in forms with a very 
simple gametophyte. 
It is in the Pteridophytes, or ferns, that the sporo- 
phyte first becomes entirely self-supporting. Here the 
embryo-sporophyte closely resembles that of the mosses, 
but soon develops the special organs, stem, root, and 
leaf, which distinguish the fern-sporophyte and render 
it independent of the gametophyte, which now withers 
away as soon as the young sporophyte is established. 
