MOSSES 



179 



It must be remembered, however, that the sperms are very 

 small and can swim in such a film of water as may be left 

 on the plant by a heavy 

 dew or rain. Since many 

 mosses grow in very dry 

 places, fertilization with 

 them must be very in- 

 frequent. When the 

 sperms are free to swim 

 they are attracted toward 

 the necks of the arche- 

 gonia, pass down them, 

 reach the egg, and fertili- 

 zation is accomplished. 



The oospore thus formed within the archegonium at 

 once ^begins to germinate (Fig. 172), and forms the spore- 

 producing structure, which in mosses is much more than a 



FIG. 174. Spore-cases of a moss, from which 

 the lids have fallen, displaying the teeth. 

 After KEENER. 



FIG. 175. Filamentous growth of the young moss: A, very young filament coming 

 from a spore (); B, older filament, showing branching habit, remains of old 

 spore (*), rhizoids (r), and buds (6) which develop the erect leafy branches. 

 After MUELLER-THURGAU. 



