12 



RESEARCHES ON FUNGI 



resulting in the production of zygophores must be caused by excre- 

 tions of the sexual substances from the ordinary vegetative hyphae, 

 while the zygotropic effect which results in ( + ) and (— ) zygophores 

 growing toward one another must be caused by excretions of the 



Fig. 4. — Zygorhynchus exponens, one of the homothallic Mucori- 

 neae. Zygophores with conjugating branches. Conjugation 

 takes place only between a ( + ) branch and a ( — ) branch. 

 In this species the ( + ) branches and the ( — ) branches are 

 different not only physiologically but also morphologically. 

 From Burgeff's Untersuchungen iiber Sexualitdt und Parasi- 

 tismus bei Mucorineen. Magnification, 80. 



sexual substances from the zygophores themselves. 1 Whether or 

 not a single pair of sexual substances is sufficient to cause all the three 

 kinds of reactions — telemorphic, zygotropic, and thigmomorphic — 

 remains to be determined. 



In a homothallic species, e.g. Zygorhynchus exponens, Absidia 



i H. Burgeff, he. cit., pp. 22-23. 



