714 AQUATIC PHYCOMYCETES 



fungi with similar zoospores, the Blastocladiales, is undoubtedly allied 

 to the Monoblepharidales. This relationship is strikingly illustrated in 

 Allomyces and Blastocladiella, where the vacuolization of the hyphal 

 cytoplasm and the development of the gametangia may at times exactly 

 resemble those of certain species of Monoblepharis. Presumably, both 

 orders stemmed from chytridiaceous ancestry but developed independ- 

 ently, with one line differing from the other particularly in method of 

 sexual reproduction and in growth habit. 



Members of Monoblepharis and Gonapodya are quite variable in 

 nature. It is frequently a difficult and puzzling matter to separate the 

 species. Even in M. hypogyna, one of the best-defined species of Mono- 

 blepharis, forms very like those of M. polymorpha or the closely related 

 M. macrandra are occasionally found. In Gonapodya individual varia- 

 tions and intergradations between the two known species may be so 

 extensive as to make specific determination impossible. Wide diver- 

 gences in size are common, and often a single plant will bear organs 

 approaching or reaching the recorded limits for the species. Size, there- 

 fore, is not considered especially significant. The fact that all their 

 features are subject to variation and that many forms are often found 

 growing together, is strong evidence that in this group (as in Allomyces) 

 hybridization has occurred between species. 



Of the two families of the order now recognized, the Gonapodyaceae 

 and Monoblepharidaceae, the former, containing Gonapodya and Mono- 

 blepharella, is clearly the more primitive. In the Gonapodyaceae, more 

 than one female gamete may be found in an oogonium and it (in Gona- 

 podya) may actually creep out and be fertilized at some distance from 

 the parent cell as happens in anisogamous planogametic reproduction. 

 Furthermore, the gametangia in that family are not so uniformly in 

 intimate contact with one another as they are in the Monoblephari- 

 daceae and the zygote undergoes a period of motility before encystment. 

 In the Monoblepharidaceae, sexuality is more strongly oogamous. A 

 single egg is formed in the gametangium, within which it is fertilized. 

 No period of motility is undergone by the zygote other than to ooze to 

 the mouth of the oogonium, and the sex organs (except in Mono- 

 blepharis macrandra) are borne in intimate contact with one another. 



