LIFE HISTORY OF A FERN 1 71 



to accomplish this they must unite, and the fusion of the 

 sperm and egg is fertilization. One of the most significant 

 facts about Jertilization 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 (sp) 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 



