160 PLANT-LIFE 



open and discharge the spores (g). In h we see the 

 spores greatly enlarged, and observe that they each bear 

 four curious arms, or elaters. The elaters are hygro- 

 scopic; in the presence of moisture they coil up (see 

 drawing), but when dry they expand. These changes 

 set the spores in motion. It is conjectured that the 

 elaters serve two purposes; in the first place, they are 



Fig. 51. — Female Prothallus of Equisetum maximum, seen from 

 Beneath, x 30. 



a, a, Archegonia; I, I, lobes; r.h., root-hairs. 



said to help in the opening of the sporangium; in the 

 second, they bring about entanglement of the spores, 

 and thus insure that they fall to the ground and ger- 

 minate in close proximity. This is essential, as the 

 prothalli rising from the spores are as a rule unisexual, 

 and if fertilization is to be secured the sexes must be 

 within easy reach of each other. Fig. 51 is a drawing of 



