LIFE CYCLES, SEXUALITY, AND SEXUAL MECHANISMS 



69 



nioncs, \\ere first demonstrated in the fungi, by Burgcff in 1924, in 

 Ahicor vnicedo, a close relative of "black bread mold." Since that 

 time sexual hormones have been demonstrated or postulated on good 

 experimental evidence in various groups of fungi exclusive of Basidi- 

 omycetes (Backus, 1939; Bishop, 1940; Krafczyk, 1935; Raper, 1939, 

 1940, 1951, 1952; Zickler, 1952). In only a single case, however, has 

 an understanding of the over-all role of hormones as the coordinating 

 agents in the sexual process been approached. 



? 



Vegetative Plant 



I — A- Initiates- 



The A-Complex 



Production of 

 Antheridiol Hyphoe 



\, 



B- 



/Mutually Augment 

 A- Initiates ' 



Production of 



-> 



Attraction of 

 Antheridiol Hyphoe 



Thigmotropic Response 



A/ 

 Delimitation of ^ 



Antheridia 



Oogonio 



Initials 



d; 



-> 



■> 



Delimitation of 

 Oogonia 



Differentiation of 

 Oospheres 



-Fertilization 



-> 



V 



Maturation of 

 Oospores 



Fig. 8. The hormonal mechanism that coordinates the sexual interaction 

 between male and female plants in heterothallic species of Achlya. Each line 

 designated by a letter indicates a specific hormone, its origin, and its specific 

 activity. (From Raper, 1951.) 



