1196 Wisconsin Academy of Sciences, Arts, and Letters. 
concluded that the production of zygospores is influenced by 
the medium on which they are grown. Zopf (1888) attributed 
their formation to the invasion of parasites which caused a 
decrease in the number of sporangia produced. Klebs (1898, 
1902) attributed the immediate cause of sporangial formation 
to transpiration, the stimulus for zygospore production being 
concerned with decreased transpiration. Falck (1901) claimed 
that zygospores would form only when the concentration of the 
medium is high and that the relative humidity is of slight, if 
any, importance. 
Blakeslee (1904) confirmed Klebs’ results showing that in¬ 
creased moisture favors the formation of zygospores. He also 
showed that the concentration of the medium is unimportant. 
Blakeslee came to the conclusion, however, that these various 
physical factors were but secondary influences and that pure 
sexual strains existed upon which zygospore production was 
primarily dependent. He obtained cultures of Rhizopus nig¬ 
ricans from mycelia which had developed from the suspensors 
of a zygospore and succeeded in isolating two pure strains 
which, when grown alone through numerous generations, gave 
rise to sporangial growth only. If they were ‘ ‘ contrasted, ’ 7 
that is, grown side by side, or in mixed cultures, they readily 
produced zygospores. Thus the heterothallic nature of 
Rhizopus nigricans was established. Later he extended his work 
to include Absidia caerulea, Phycomyces nitens, Mucor mucedo, 
and several undetermined Mucors, among the heterothallic 
forms. 
Blakeslee’s results have not been extensively tested by other in¬ 
vestigators. Hamaker (1906) claimed that zygospores of 
Rhizopus nigricans could be produced unfailingly upon proper 
media. Namyslowski (1906) also believed that the nutrients 
were responsible for zygospore production. 
The writer (1914) in an earlier paper reviewed rather com¬ 
pletely the literature relevant to the cytology of conjugation in 
the Mucorineae. 
The results of studies upon Sporodinia grandis published by 
the writer (1914) vary but little from those published by 
Dangeard (1906) in his later paper. Fusions in pairs appear 
to take place between the nuclei of the fusing gametes. Cer¬ 
tain plastid-like bodies apparently concerned with the produc- 
