FILICES 



67 



archegones being produced later, and in smaller numbers, on female pro- 

 thallia ; or the same prothallium may produce first antherids and sub- 

 sequently archegones, when it may be termed proterandrous. This is 

 remarkably the case also in Gymnogramme. In Cystopteris fragilis 

 (Bernh.) (Polypodiace^e) Campbell states that there are two kinds of 

 prothallium, a smaller male and a larger hermaphrodite. The prothal- 

 lium of ferns is sometimes propagated vegetatively by the production of 

 adventitious shoots from single marginal cells, which become detached 

 and form independent prothallia. This takes place especially in 

 Hymenophyllacece and in Osmunda, but occurs also in Polypodiaceae, 



Fig. 45. — Archegone o? Adiantum capillus-Veneris, in various stages. A,B, C, E, in longitudinal, 

 D, in transverse section ; A, neck ; si, canal-cells converted into mucilage ; s, ventral canal-cell ; 

 e, oosphere ; in E divided into a 2-celled embrj-o (x 800). (After Goebel.) 



abundantly in Gymnogramme (see Cramer, Denkschr. Schweiz. Naturf. 

 Gesell., 1880). The prothallium of Yittaria (Sm.) produces peculiar 

 stalked bulbils. 



The antherids of ferns are small papilliform projections on the 

 under side or margin of the prothallium (very rarely on the upper side), 

 produced among the rhizoids, and of similar origin, i.e. from a single 

 superficial cell ; in the Hymenophyllaceae they are produced also on 

 the protonemal filaments. The protuberance becomes separated by a 

 septum from the parent superficial cell, and then sometimes divides at 

 once into the parent-cells of the antherozoids. But more often the 



F 2 



