FERNS 



195 



spirally coiled bodies, blunt behind and tapering to a beak 

 in front, the beak bearing numerous cilia (Fig. 188). The 

 fern sperm, therefore, is a large, spirally coiled, multiciliate 



Fro. 188. Two antheridia of a fern (A), one containing sperms, the other discharg- 

 ing them; also a single sperm much enlarged (B). 



sperm, as compared with the small biciliate sperm of Bry- 

 ophytes. 



With a ciliated sperm, fertilization can be effected only 

 in the presence of moisture, and if prothallia are kept dry 

 fertilization does not occur. In nature, however, the pro- 

 thallia lying prostrate on the substratum are in a favor- 

 able position for moisture; and when there is a film of mois- 

 ture between the prothallium and the substratum the 

 sperms can swim to the archegonia. 



The oospore which is produced germinates at once and 

 forms the leafy sporophyte (Fig. 186, B}. The young stem 

 and the root remain under the soil, but the young leaf is 

 seen curving upward through the notch of the prothallium 

 and growing up into the air and light. For a short time the 

 young plantlet absorbs nourishment from the prothallium, 

 but with its own root system and leaves it soon becomes 



