484 



General Botany 



ical species new plants develop vegetatively from the swollen 

 leaf bases. 



The sporophyte. The familiar fern plant is the sporophyte. 

 In many species the foliage leaves develop groups of fruiting 

 bodies called sori (singular, sorus), on the under surfaces of the 

 later leaves. Each sorus consists of several or many sporangia, 

 and within each sporangium from 32 to 64 spores develop. In 

 the cinnamon fern the fertile leaves differ from the foliage leaves, 



being reduced in size, without 

 chlorophyll, and with the leaf- 

 lets (pinnae) acting merely as 

 supports of sporangia. Special 

 spore-bearing leaves are called 

 sporophylls. An average fern 

 plant in this way produces 

 several to many million spores 

 each season. 



The gametophyte. The 

 spores germinate either im- 

 mediately, or after a dormant 

 period. From them there de- 

 velops a small, heart-shaped 

 thallus that superficially re- 

 sembles a liverwort. This is 

 called the prothallus, and con- 

 stitutes the gametophyte gen- 

 eration of the fern. Prothalli 

 may be found commonly on 

 moist rocks, or on the soil 

 near fern plants. 



As the flat expanse of cells 



forming the prothallus de- 



r, ^ ^ , velops, rhizoids appear on the 



Underground stem, roots, and 



leaves of a fern. lower sidc ; and soon af ter- 



FlG. 299. 



