THE EVOLUTION OF PLANT REPRODUCTION 



65 



develop sporangia filled with microspores, which grow into male 

 prothalli. 



SPORANG/UM (POLLEN SAC) 



MALE CONE 



MICROSPORE MALE GAMETQPHrTE 



PEMALE GAMETOPHYTE 



FEMALE CONE 



Fig. 38. — The pine sporophyte develops two kinds of cones; one produces 

 small spores which germinate into male gametophytes and the other produces 

 large spores which germinate into female gametophytes. 



Reproduction begins when the male cones release their micro- 

 spores, often in clouds which float in the air like dust particles. 

 Carried by gravity or wind, a few chance to alight on the female 

 cones. A microspore which has fallen among the scales of the 



