MU COR ALES 239 



identical. For such cases he prefers the term syngamy (syn- 

 gametic). Blakeslee (1906 b) feels that the similarity of the 

 gametangia does not in the least detract from his conclusion that 

 the differentiation into (+) and ( — ) strains is a sexual one. He 

 points out that the use of the term isogamy (the conjugation 

 of equal gametes in which no differentiation of sex can be dis- 

 tinguished) has only a morphological application among the 

 Mucorales, since sexually the two gametangia which unite have 

 diametrically opposite characters. The mutual indifference of 

 two mycelia of the same sex and the active sexual reaction 

 between mycelia of opposite sex which leads to the formation of 

 zygospores when the mycelia are of the same species, indicate 

 that the gametes are fundamentally different. In no species, 

 however, either homothallic or heterothallic, in which the 

 process of conjugation has been carefully followed, do the 

 progametangia grow toward each other as has been commonly 

 believed. They arise from the stimulus of actual contact 

 between hyphae which touch each other, and are from the very 

 beginning adherent. 



In order to determine the sexual identity of the ( + ) and ( — ) 

 strains, and to enable him to substitute the terms male and 

 female, Blakeslee (1913; 1915) has performed some interesting 

 experiments. In the heterothallic group no species has been 

 discovered in which the gametangia differ constantly in mor- 

 phology. The differences in size occasionally noted in Rhizopus 

 nigricans and others are neither constant nor correlated with 

 the (-(-) and ( — ) condition. In the homothallic group several 

 well known species are heterogametangic, the gametangia differing 

 strikingly in size and shape. To this category belong Zygorhyn- 

 chus moelleri, Zy. heterogamus, Absidia spinosa, and Dicranophora 

 fulva. Blakeslee feels that from analogy with the Oomycetes 

 the larger gametangium may be considered female and the smaller 

 male. Upon this basis if a sexual reaction could be established 

 between these unequal gametangia and the ( + ) and ( — ) strains 

 of a heterothallic species, the strain reacting with the larger 

 female cell would be considered male, and that reacting with 

 the smaller male cell would be considered female. Only a single 

 heterogametangic species (Absidia spinosa) was found which 

 would give reactions with both ( + ) and ( — ) strains, and only 

 a single heterothallic species {Mucor hiemalis) which would 

 react with both male and female gametangia of this heterogamic 



