LIFE HISTORY OF A FERN 
175 
organism similar to that with which we started a full- 
grown fern-plant, capable of producing spores, which can 
develop into prothallia again, with antheridia and arche- 
gonia, producing sperms and eggs, and so on. Thus we 
see that the steps in the life history of a fern constitute 
a life-cycle. At whatever point or with whatever struc- 
ture we start, if we follow the course of development we 
are brought back again to the same point, or the same 
kind of structure with which we began. 
FIG. 132. Prothallia of a fern, i, Before the sporophyte had appeared; 
2-5, with sporophytes attached; /, cotyledon or first leaf of the sporophyte; 
v, circinate vernation of a leaf; s, mass of soil adhering to the rhizoids and 
roots. 
160. Simpler Ferns. In addition to the leptosporan- 
giate ferns, which have served as a basis for the general- 
ized description given above, there is another group, 
having a more primitive type of organization. Repre- 
sentatives of this group include the "moonworts" (species 
of Botrychium, Fig. 133), and the "adder's tongue" 
(Ophioglossum vulgatum, Fig. 134). The species of 
