16 RESEARCHES ON FUNGI 



are really the chemomorphic and zygotropic agents which bring 

 about fusions of the peg-to-peg type (cf. Fig. 15, p. 31), these 

 substances can have nothing to do with sex. 



In 1928, Laibach 1 compared the vegetative hyphal fusions 

 which are found in the mycelia of two Ascomycetes, Leptosphaeria 

 Coniothyrium and Monilia fructigena, with the fusions that take 

 place between the sporidia of species of Ustilago, e.g. Ustilago bromi- 

 vora, and he came to the conclusion : " that important physiological 

 differences between the fusions investigated in the Ascomycetes 

 and those which occur in the Ustilagineae do not exist ; and that 

 from the physiology of the fusion of sporidia in the Smut Fungi no 

 argument for the sexual nature of the phenomenon can be drawn ; " 

 and he accepted the view of Boss 2 that, when two Smut sporidia 

 unite, one should not speak of the copulation of sporidia, but should 

 employ Brefeld's non-committal term fusion. However, against 

 Laibach's conclusion may be urged, in respect to fusions, that, 

 whereas in Leptosphaeria Coniothyrium, Monilia fructigena, Tricho- 

 derma lignorum 3 and other Ascomycetes the germ-tubes or young 

 mycelia derived from any two spores of the same species may unite, 

 in Ustilago violacea and certain other Smuts there are two kinds of 

 promycelial cells of such a nature that union takes place between a 

 descendant (sporidium or sprout-cell) derived from one kind of cell 

 and a descendant derived from the other kind of cell, but not between 

 descendants of the same cell or of two cells of the same kind. 4 There 

 seems no good reason why, with Kniep, we should not regard the 

 fusions between sporidia in Smut Fungi as essentially sexual in 

 their physiological nature rather than as vegetative. 



Laibach 5 came to the conclusion that action at a distance 

 between hyphae destined to fuse is exhibited by both Ascomycetes 

 and Ustilagineae ; and he remarked that " in both groups it appears 



1 F. Laibach, " Uber Zellfusionen bei Pilzen," Planta, Bd. V, 1928, pp. 340-359. 



2 G. Boss, " Beitrage zur Zytologie der Ustilagineen," Planta, Bd. Ill, 1927, 

 p. 642. 



3 Vide these Researches, Vol. IV, 1931, Figs. 98 and 100, pp. 173 and 176. 



4 H. Kniep, " Untersuchungen iiber den Antherenbrand," Zeitschriftfiir Botanik, 

 Bd. XI, 1919, pp. 257-284 ; also Die Sexualitat der niederen Pflanzen, Jena, 1928, 

 pp. 429-430. 



5 F. Laibach, luc. rit., pp. 356-357. 



