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 

 FIG. 234. Development of the fern gametophyte 



the careless ob- 



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

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

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

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

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

 a much smaller scale than the others. All considerably 

 enlarged 



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. 



