74 RESEARCHES ON FUNGI 



suggests that in these strains taken altogether there are a consider- 

 able number of differently constituted nuclei. Possibly much of the 

 variation in Botrytis strains is due to sudden change in nuclear 

 structure. 



Miiller, 1 who has observed .that, in Hypochnus solani (=Rhizoc- 

 tonia solani), the mycelium is diploid from the first, that several 

 nuclei divide conjugately in the terminal cell of each growing hypha, 

 and that hyphal fusions take place frequently between the hyphae 

 of any two monosporous mycelia, has suggested, with the help of 

 diagrams, that sometimes a nucleus may pass from a hypha of one 

 strain, which we may call (A), through the passage-way of a hyphal 

 fusion into a hypha of another strain, which we may call (B), and 

 there divide conjugately with several (B) nuclei, so that in the end, 

 in some or all of the young basidia of a fruit -body produced on the 

 (B) mycelium, fusions may take place between (^4) and (B) nuclei, 

 thus making the production of a hybrid strain possible. This 

 suggestion, to which no theoretical objection applies, so far has not 

 been brought to the test of experiment. 2 



1 K. 0. Muller, " Untersuchungen zur Entwicklungsgeschichte und Biologie von 

 Hypochnus solani P. u. D. (Rhizoctonia solani K.)," Arbeiten aus der Biologischen 

 Reichsanstaltfur Land- und Forstwirtschaft, Bd. XIII, 1924, pp. 216-221. 



2 In a paper which has come to hand during the reading of the proofs of this 

 chapter, S. Dickinson (" The Nature of Saltation in Fusarium and Helmintho- 

 sporium," University of Minnesota Ayr ic . Exp. Sta. Tech. Bull., No. 88, Nov., 1932, 

 pp. 1-42, Text- figs. 1-6) records that, employing microscissors, he cut out hyphae 

 from mycelia of species of Helminthosporium and Fusarium and mated them side 

 by side on agar. Under these conditions, he found that, in Fusarium, hyphal 

 fusions " were more easily induced between cells of the same strain, or between 

 cells of closely related strains, than between cells with a more distant relationship." 

 Fusion cells formed between pairs of cells of two contrasting saltant strains of 

 Fusarium fructigenutn, after isolation, produced hyphae which, after isolation, 

 developed into mycelia showing the characteristics of one or other of the parent 

 forms and not of any new form. On the basis of (1) these and other experiments 

 and (2) a cytological investigation, Dickinson has come to the conclusion that 

 heterocaryosis arising through hyphal fusions cannot account for the phenomenon 

 of saltation in the mycelia of the species which he studied. 



