282 



PRACTICAL BOTANY 



annulus opens outward. The capsule is torn open at the mouth, 

 and its entire upper half may thus be turned back with the 

 annulus ; this occurs so slowly that part or all of the spores 

 within the upper part of the sporangium may be carried back 

 within it. The annulus becomes tense, like a tightly drawn 



elastic spring,- 



then flies again 

 into its original 

 position, and in 

 so doing throws 

 spores with con- 

 siderable force. 

 By mounting spo- 

 rangia under a 

 low-power micro- 

 scope, moistening 

 them, and then 

 watching them 

 as they become 

 dry, their action 

 will be seen; but 

 the closing of the 

 sporangia often 

 happens so sud- 

 denly as to elude 

 the careless ob- 

 server, and the 

 spores are usu- 

 ally thrown so 

 far that they are 

 altogether lost. 



Since these spores are formed within a capsule by division of 

 the tissues, it is clear that they are asexual spores. The com- 

 plex leafy fern plant is the sporophyte, since it forms asexual 

 spores. It produces these in very large numbers, thus providing 

 abundantly for possibilities of gametophyte production. 



Fig. 234. Development of the fern gametophyte 



A, an asexual spore; S and C, asexual spores germinat- 

 ing, each having produced a green filament and a rhizoid ; 

 D, the hroadening of the green filament and the differ- 

 entiation of an apical cell (a) ; E, a well-formed fern 

 gametophyte ; D and B are diagrams and E is made on 

 a much smaller scale than the others. All considerably 

 enlarged 



