LIFE HISTORY OF A FERN 
171 
to accomplish this they must unite, and the fusion of the 
sperm and egg is fertilization. One of the most significant 
facts about fertilization in ferns is that free water is re- 
quired, in order that the sperms may reach the egg by their 
own locomotion. When the antheridia and archegonia 
are mature, a suitable amount of water (such as would 
result from a rain or a copious dew), soaking through the 
FIG. 129. Fern prothallus; cross-sections showing antheridia (an), 
sperms (sp), and rhizoids (rh). Below at the right is a sperm (s/>) greatly 
enlarged. 
archegonial walls, will cause the mucilaginous matter in 
the neck-canal to swell. This in turn will rupture the 
archegonia at their distal ends, and a portion of the con- 
tents of the neck-canal will become extruded, while the 
egg will remain in the venter. The same conditions of 
moisture will cause the rupture of the antheridia, and the 
sperms will be set free (Fig. 129). The mucilaginous matter 
