290 ASSOCIATIVE EFFECTS AMONG FUNGI 



generally in connection with reproductive activities among hetero- 

 thallic fungi. Recently .Moreau and Aloruzi (1931) claimed that 

 perithecia of Neurospora are produced if two strains are grown 

 in opposite ends of a U-tube, and that this response is the result 

 of diffusion of a hypothetical hormone through the medium from 

 one arm of the tube to the other. Dodge (1931) attempted to 

 repeat their experiments with Neurospora sitophila and N. tetra- 

 sperma but did not succeed in obtaining perithecia unless and 

 until the hyphae of opposite colonies were in contact. Raper 

 (1939, 1939a, 1940) presented evidence that the sexual reactions 

 in Achlya bisexualis and A. ambisexualis are controlled by four 

 specific substances, two produced by the male mycelia and two by 

 the female. Responses are evident when the mycelia are 6 mm 

 apart, if mated on agar. Both sex strains are activated when 

 grown on opposite sides of a cellophane membrane. Male plants 

 form antheridial branches when placed in water in which female 

 plants have previously been grown. Furthermore, female plants 

 produce oogonial initials when placed in water in which male 

 plants have been grown and have formed antheridial branches, 

 although there is no such activation in water in which a vegetative 

 male has been grown. Of the two hormones produced by the 

 female plant, one initiates the formation of antheridial branches, 

 and the other, in connection with a thigmotropic response, in- 

 duces the delimitation of antheridia. Of the two hormones pro- 

 duced by the male plant, one initiates the formation of oogonial 

 branches, and the other brings about the delimitation of the 

 oogonium. The chemical constitution of none of the hormones 

 is yet known. 



The filtrate of old cultures of Aspergillus niger contains a prin- 

 ciple that promotes conjugation of Zygosaccharomyces acld'i- 

 jaciens [Nickerson and Thimann ( 1943) ]. This principle, on be- 

 ing fractionated, appears to consist of an organic acid and a mem- 

 ber of the vitamin B complex, neither fraction having much 

 activity by itself. Nickerson and Thimann were unable to iden- 

 tify these constituents with certainty, but when they imitated the 

 principle by a mixture of glutaric acid and riboflavin, conjugation 

 was promoted. 



Synergetic reactions. Synergism or svnergetic reaction logi- 

 cally appears to be a form of stimulation, the term applying, how- 

 ever, only to cooperative phenomena that might not be produced 



