SEXUAL REACTIONS BETWEEN MUCORS. 95 



spinosa and the sexual races of Mucor V., one would seem 

 justified in considering the vegetatively more vigorous ( + ) 

 race as female, and the less vigorous ( ) race as male. The 

 terms male and female therefore may be used hereafter in dis- 

 tinguishing the sexual races of dioecious Mucors. 



REACTIONS BETWEEN DIOECIOUS SPECIES AND ZYGORHYNCHUS. 



Zygorhynchus Moelleri shows no sexual reaction with the ( ) 

 race of Mucor V. but contact with its ( + ) race causes the pro- 

 duction of delicate, contorted, warty filaments which take part 

 in imperfect hybridizations as shown in Fig. 12. The gametes 

 formed by Z. Moelleri in contact with Mucor V. ( + ), fre- 

 quently are transformed into azygospores shown in Fig. n. Z. 

 Vuillemini apparently is identical with Z. Moelleri, at least so 

 far as its sexual reactions with Mucor V. are concerned. 



In contrast with these two Zygorhynchus forms just discussed 

 which show only a ( ) or male tendency in contact with Mucor 

 V., Z. heterogamus gives evidence of a female tendency. Its 

 reactions with the ( ) race of Mucor V. are shown in Figs. 25-28. 

 It does not seem to react with ( + ) races and even with the 

 ( ) race it is not easy to induce reactions and those that result 

 do not lead to azygospore formation. If Mucor V. ( ) in 

 Fig. 25 is actually showing a sexual reaction with the male gamete 

 of Z. heterogamus as might appear from its position on the termi- 

 nal filament of the latter, the evidence would be in conflict with 

 that to be drawn from the reactions with A. spinosa, i. e., that 

 the ( ) race is male and the ( + ) race female. It will not be 

 possible to attach much significance to the individual reactions 

 in Zygorhynchus, however, since so far no form of this genus 

 has been induced to react with more than a single sexual strain 

 of the test dioecious species. 



Z. Vuillemini var. agamus is a zygosporeless strain which Xamy- 

 slowski (10) separated from a culture of Z. Vuillemini. It was 

 found impossible to induce zygospore formation from cultures 

 of this species supplied by the Centralstelle. In contact with 

 the ( + ) race of Mucor V. (Figs. 30-32) however, it reacted 

 like the sexually active strain of Z. Vuillemini and even pro- 

 duced azygospores (Fig. 32). This form therefore has a male 

 tendency. 



