ELEMENTARY STUDIES OF 



275 



part in the life-history of a fern which may be compared to 

 a flower of a flowering plant, because it bears on its under 

 side the organs corresponding to pollen and ovules, and it 

 is from the under side of this prothallus that the leafy fern 

 arises (Figs. 155 and 156). 



The arrangement of these spore masses is very definite 

 in the different ferns and is made the basis of classifica- 

 tion. Pupils might verify some of the following points. 



(a) The groups of brownish 

 spore masses (sori) are not covered 

 by a membrane (indusium) in the 

 common Polypody, Oak fern, or 

 Beech fern. 



(6) The spore clusters (sori) are 

 on the under side of the pinnules 

 and are covered by an indusium. 

 Examples : Male fern, (indusium 



is kidney -shaped). 

 The Bladder fern (indusium, 

 bladder- like) . 



(Q) The spore clusters (sori) are 

 on the back of the fronds, linear in 

 form ; the indusia are scale-like. 

 Examples : The Lady fern, with 

 many small sori, variously curved 

 in outline ; the Maiden- hair spleen- 

 wort, with numerous short sori, 

 crowded and becoming COM fluent, 



the indusium pale brown, free, with entire edges ; the 

 Hart's-tongue with linear sori parallel at right angles to 

 midrib. 







(d) The spore clusters (sori) are upon the margin of the 

 frond, which is recurved upon them. Examples : Maiden- 

 hair fern, Hard fern, and Bracken. 



(e) In the Moonwort and Eoyal fern the spore clusters 

 are grouped in inflorescence-like masses. 



Fig. 156. Young Fern still at- 

 tached to the Prothallus, 

 growing from an arche- 

 gonium. 



