52 



PHYCOMYCETEAE 



and delimitation of walled uninucleate cells the parasite becomes a 

 "soms." These cells may remain thin-walled and polyhedral by mutual 

 pressure or may round up and become separate, with thicker walls. 

 Within each of these cells the nucleus divides until a large number 

 (sometimes hundreds) are present. As these sporangia enlarge, the whole 

 cell is ruptured and the sporangia themselves escape separately, as in 

 S. decipiens (Peck) Farlow, or rupture within the host cell releases the 

 swarm spores. In many species the original fungus cell does not directly 

 become the sorus of sporangia but while still in the uninucleate condition 

 buds out into a thin-walled sorus in the outer part of the host cell, the 

 sporangia and swarm spores being formed in this sorus instead of in the 

 original cell, w^hich in this case is called a prosorus. 



The swarm spores may infect the host directly or may unite by twos, 

 forming biflagellate zygotes which settle on the epidermis of the host 

 and encyst, the nuclei then fusing. The host cell is then entered and after 

 some growth the parasite becomes a thick-walled resting spore. After a 

 longer or shorter period this may function directly as a sporangium, or 

 as a sorus of sporangia, or as a prosorus, releasing swarm spores which 

 infect the host asexually or after sexual union with other swarm spores. 

 In some species there are several generations in a season, at least of the 

 asexually produced individuals, while in others only the thick-walled 

 overwintering generation is known. Whether this is asexually or sexually 

 produced has not been determined. Sexuality has been demonstrated for 



Fig. 12. Cliytridiales, Family Syncliytriaceac. Synchytrium fulgrns Schroet. 

 (1-8) Summer cycle. (I-VIII) Winter cycle. (After Kusano: Japanese J. Botany, 

 5(1):35-132.) 



