FERNS. 



171 



under side uppermost, we can then examine it for the sexual 

 organs, for these are borne in most cases on the under side. 



Fig. 144. Fig. 145. 



Section of antheridia showing sperm cells, and spermato- Different views of spermatozoids; 

 zoids in the one at the right. in a quiet condition ; in motion 



(Adiantum concmnum). 



281. Antheridia. If we search among the rhizoids we see 

 small rounded elevations as shown in figure 139 scattered 

 over this portion of the prothallium. These are the antheridia. 

 If the prothallia have not been watered for a day or so, we may 

 have an opportunity of seeing 

 the spermatozoids coming out 

 of the antheridium, for when 

 the prothallia are freshly placed 

 in water the cells of the antheri- 

 dium absorb water. This presses 

 on the contents of the antheri- 

 dium and bursts the cap cell if 

 the antheridium is ripe, and all 

 the spermatozoids are shot out. 

 We can see here that each one 

 is shaped like a screw, with the 

 coils at first closed. But as the 

 spermatozoid begins to move 

 this coil opens somewhat and 



Fig. 146. 



Archegonium of fern. Large cell in 

 the venter is the egg, next is the ventral 

 canal cell, and in the canal of the neck 

 are two nuclei of the canal cell. 



by the vibration of the long cilia which are on the smaller end it 

 whirls away. In such preparations one may often see them 

 spinning around for a long while, and it is only when they 

 gradually come to rest that one can make out their form. 



