440 PTERIDOPHYTES (FERN PLANTS) 
The strobilus, therefore, arose as a result of differentiating the 
leaves in function and aggregating the sporophylls. Differing in 
function, sporophylls and vegetative leaves would come to differ 
inform. One can see considerable advantage in this to the plant. 
It permits a large amount of leaf tissue to be devoted entirely to 
the manufacture of food, while the sporophylls, since they are 
not depended upon for food, can be much crowded, and as a result 
many spores can be produced on a small region. In scattering 
the spores there is also an advantage in having the sporophylls 
at the top of the stem. 
Gametophyte. — When the spores fall to the ground and 
germinate, they develop fleshy gametophytes consisting usually 
of a tuberous subterranean portion from which small, aérial, 
green lobes arise on which the sex organs are produced. Within 
Fic. 393. — The sporophyte of a Selaginella. After J. M. Coulter. 
the tissues of the gametophyte there lives a filamentous Fungus, 
and thus it is seen that the gametophyte resembles the gameto- 
phyte of Botrychium in a number of ways. 
The fertilized egg begins to develop immediately after fertiliza- 
tion, and the young sporophyte is soon formed and the life cycle 
thus completed. 
Selaginella. — The Selaginellas, known as Little Club Mosses. 
are widely distributed over the world and are common in con- 
servatories where they are grown under the benches, in pots, and 
in hanging baskets for their decorative effect. 
