THE FERNS 125 
especially well developed upon the leaves, where it is 
furnished with stomata communicating with the green 
tissue of the leaf, and also is often provided with hairs 
and scales of characteristic form. The remaining tissue, 
usually known as the “ground-tissue,” shows a much 
greater diversity of structure than is met with in any of 
the lower plants, and closely approaches in this respect 
the higher flowering plants. 
While in the mosses the existence of the sporophyte 
usually ends with the dispersal of the spores, in the 
ferns spore-formation is subordinated to the vegetative 
existence of the sporophyte. The spores themselves, 
instead of arising from a large, continuous archesporium, 
are here restricted to certain definite structures of the 
sporophyte called sporangia (Figs. 34, 35). A faint 
indication of this segregation of the sporogenous tissue 
is seen in the Anthocerotacee, among the liverworts, 
where there is an imperfect separation of small sporo- 
genous areas by means of sterile tissue between them. 
In the ferns, as a rule, the development of spores 
usually takes place only after the sporophyte has 
reached an advanced stage of development, and this 
is often not accomplished for many years in some of 
the large ferns, although in a few cases the sporophyte 
lives but a single season. 
A study of the development of an individual case 
illustrates very clearly the homologies which exist be- 
tween ferns and the lower mosses. It is well known 
to botanists that the germinating fern-spore does not 
at once produce the leafy sporophyte, but there is first 
formed a much simpler plant, the gametophyte (Fig. 32). 
On first germinating, the unicellular spore usually pro- 
