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 
Fic. 188.—Two antheridia of a fern (.4), 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 odspore 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 ashort time the 
young plantlet absorbs nourishment from the prothallium, 
but with its own root system and leaves it soon becomes 
