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 prothaUia 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. — ProthaUia of a fern, i, Before the sporophyte had appeared; 

 2-5, with sporophytes attached; I, 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 vulgatunij Fig. 134). The species of 



