(,M) AQUATIC PHYCOMYCETES 



sporophyte or gametophyte. She suggested the chemical may cause 

 separation of the chromosomes into two groups during mitosis without 

 their splitting. 



GENETICAL STUDIES 



The genetics of Allomyces has been investigated experimentally. The 

 major part of the work up to the present has been done by Emerson 

 (1941) and by Emerson and Wilson (1954) and deals especially with 

 hybridization and inheritance among members of the Euallomyces 

 group. It will be seen from Figure 40 A-B (p. 616) that a well-marked 

 and opposing arrangement of the gametangia may exist on the game- 

 tophyte plant, that is, in A. arbuscula the male is hypogynous and 

 the female epigynous, whereas in A.javanicus, on the contrary, the 

 male is epigynous and the female hypogynous. Interspecific crosses 

 were successfully made and the inheritance of the gametangial ar- 

 rangement followed in the haploid (gametophyte) generation. This 

 particular procedure was necessary because the sporophytes of the 

 two species showed no striking differences. In this respect the stud- 

 ies, therefore, differ from those carried out on higher plants in 

 which the inheritance of characters of the diploid generation is followed. 

 The interested reader is referred directly to the extensive and careful 

 elucidation of the methods given in Emerson and Wilson's paper, which 

 will undoubtedly serve as a model for future work of a similar character. 



Emerson and Wilson summarize their findings as follows: 



Reciprocal matings made between four strains of A. arbuscula und three 

 of A. javanicus in various combinations show that the reaction of the gametes 

 and the percentage of "takes" vary according to the particular parents used. 

 Counts of epigyny (E) and hypogyny (H) in the gametophytes derived from 

 over a hundred F x sporophytes have demonstrated that, in addition to both 

 the parental types (E and H), a whole series o\' intermediate strains (I) segre- 

 gate out. From these results it is concluded that the arrangement of game- 

 tangia is controlled either by more than one pair of independently segregating 

 alleles or by a single pair of duplicated alleles that segregate independently. 

 The viability of meiospores from F x sporophytes is shown to be reduced to 

 less than one tenth that of the parents. 



In about one-rifth of the crosses all of the progeny exhibited pure hypogyny 

 (H). For the following reasons we believe that hybridization failed to occur 

 in these instances, the (F x ) sporophyte having arisen by parthenogenetic 



