THE FORMATION OF HYPHAL FUSIONS 23 



closely related Mucor species or possibly different forms of a single 

 Mucor species, and Burgeff J obtained zygospores when he crossed 

 Phycomyces nilens and P. Blakesleeanus . Kniep 2 (Figs. 11 and 12), 

 Dickinson, 3 and Bauch 4 all observed fusions between sporidia or 

 sporidial hyphae of different species or races of Ustilago. Hanna 

 and Popp 5 obtained smut spores as a result of crossing Ustilago 

 avenae and U. levis ; while Flor, 6 and subsequently Hanna, 7 obtained 

 bunt balls as a result of crossing Tilletia tritici and T. laevis. The 

 fact that B. 0. Dodge 8 obtained hybrids by crossing Neurospora 

 sitophila and N. tetrasperma seems to indicate that these species 

 must fuse with one another, although such fusions were not definitely 



citation, p. 43) states that Blakeslee regards the supposed species as different forms 

 of one and the same species. 



1 H. Burgeff, " Uber Arten und Artkreuzung in der Gattung Phycomyces Kunze," 

 Flora, Bd. CVIII and CIX (Goebel-Festschrift), 1925, pp. 40^6* The zygospores 

 germinated and gave rise to sporangia. 



2 H. Kniep, " Uber Artkreuzungen bei Brandpilzen," Zeit. f. Pilzkunde, Bd. X, 

 1926, pp. 217-251 ; also Die Sexualitat der niederen Pflavzen, Jena, 1928, p. 431. 

 In the genus Ustilago, as a result of pairing sporidia, Kniep found that he could 

 obtain fusions : (1) between any two species with reticulate spores (U. violacea, 

 U. Scabiosae, U. Cardui, U. vtriculosa, U. vinosa, U. anomala, and U. Tragopogonis); 

 (2) between any two species with smooth or punctate spores (U. longissima, U. 

 longissima var. macrospora, U. grandis, U. bromivora, U. Hordei, and U. perennans) ; 

 but (3) not between a species with reticulate spores and a species with smooth or 

 punctate spores. The promycelia of U. nuda and U. Tritici, which do not produce 

 sporidia, fused with sporidia of l J . Hordei, and U. bromirora. 



3 S. Dickinson, " Experiments on the Physiology and Genetics of the Smut Fungi, 

 Hyphal-fusion," Proc. Roy. Soe. (B), Vol. CI, 1927, p. 133. Dickinson observed the 

 fusion of a sporidial hypha of Ustilago levis (Covered Smut of Oats) with a sporidial 

 hypha of U. Hordei (Covered Smut of Bade) 7 ) and the passage of a nucleus through 

 the open channel from one cell to the other. 



4 B. Bauch, " Bassenunterschiede und sccundare Geschlechtsmerkmale beim 

 Antherenbrand, ,, Biol. Centralb., Bd. XLVII, 1927, pp. 370-383. Bauch found that 

 strains of Ustilago violacea obtained from Diantltus deltoides, Melandryum album, and 

 Malachium aquaticnm can be crossed and that the conjugated sporidia give rise to 

 germ-tubes. 



5 W. F. Hanna and W. Popp, " Relationship of the Oat Smuts," Nature, Nov. 29, 

 1930. 



6 H. H. Flor, " Heterothallism and Hybridization in Tilletia tritici and T. levis," 

 Journ. Agric. Research, Vol. XLIV, 1932, pp. 49-58. 



7 W. F. Hanna, " The Odor of Bunt Spores," Phytopathology, Vol. XXII, 1932, 

 pp. 978-979. 



8 B. O. Dodge, " Production of Fertile Hybrids in the Ascomycete Neurospora," 

 Joimi. Agric. Research, Vol. XXXVI, 1928, pp. 1-14. 



