62 PLANTS AND MAN 



sperm cells, while the megaspores develop into female prothalli 

 producing only eggs. Another striking comparison lies in the fact 

 that the gametophytes are microscopic, lack chlorophyll, and 

 pass their entire existence within the confines of the microspore 

 or megaspore wall (fig. 36). The microspore, while still in the 

 sporangium, grows into the simple few-celled male gametophyte, 

 which at maturity produces antheridia and sperm cells. At the 

 same time the megaspore, also while still in its sporangium, de- 

 velops within itself the tiny female gametophyte with a few 

 archegonia. 



YOUNG- 

 SPERM 



SPORE WALLS 



FEMALE PLANT MALE PLANT 



Fig. 36. — Male and female gametophytes of the little club moss never get 

 outside of the spore walls. 



When the sporangium containing the microspores bursts 

 open, the powdery microspores, containing the invisible male 

 prothalli, are scattered through the air. Some fall on the other 

 type of sporangia, which have opened and exposed the mega- 

 spores; these also have opened to expose the portion of the female 

 gametophyte bearing the archegonia. When this happens, the 

 microspore wall breaks open, the sperm cells are released from 

 the male prothallus and swim through the film of water — which 

 must be present if fertilization is to take place — to the nearby 

 female gametophyte in the megaspore. Fertilization is thus the 

 result of a process which brings the entire male plant to the 

 female one, eliminating the necessity for a long and perilous 



