74 AQUATIC PHYCOMYCETES 



of this process need further amplification. Thus, in none of the observed 

 occurrences is it certain that the swarmer which may form the game- 

 tangium is not also capable, if contact is not established with another 

 swarmer, of becoming transformed into a zoosporangium, that is, 

 whether it may not be potentially both a zoospore and a gamete. Fur- 

 thermore, it is not known if the gametes are formed in special game- 

 tangia or if from the first they are sexually differentiated as male 

 and female. It is of course possible that in some species a situation 

 similar to that in Synchytrium fulgens (Kusano, 1930a) prevails. In 

 this chytrid the sex of the gametes is not fixed, the active ones behaving 

 as males and the quiescent or germinated ones as females. Since un- 

 fused swarmers may function nonsexually to produce a thallus, Kusano 

 feels that they should be regarded as gametes undergoing partheno- 

 genetic development rather than as zoospores. That is, in S. fulgens 

 no zoospores are formed, only gametes capable of either sexual fusion 

 or parthenogenetic development. The sexuality of Rhizophydium appears 

 to be a step removed from the isogamous planogametic type found in 

 Olpidium and closer to the condition in S. fulgens in that at least one 

 of the gametes (and sometimes both) is generally nonmotile when con- 

 tact is established and fusion occurs. It differs from both Olpidium and 

 S. fulgens in that the swarmers themselves do not fuse. Rather, they 

 give rise after encystment to bodies which contain the gametic material, 

 that is, to gametangia at least one of which has developed a vegetative 

 system and is an immature thallus. Furthermore, even after fusion of 

 the gametes has occurred, the two gametangia remain distinct struc- 

 tures, the one eventually becoming the resting spore, the other, the 

 adherent cyst. 



Ledingham (1936) has reported evidence of the occurrence in Rhi- 

 zophydium graminis, a parasite on the roots of certain grasses, of another 

 type of sexuality. In this fungus anastomosis of the rhizoids has been 

 detected, although the actual fusion of the gametes was not witnessed. 

 The same investigator has also reported that fusion of zoospores takes 

 place in R. graminis, but he does not describe the fate of these fused 

 swarmers. 



Evidence for a sexual process in Diplophlyctis intestina involving 

 rhizoidal anastomosis of immature thalli was presented by Sparrow 



