90 RESEARCHES ON FUNGI 



is a curious phenomenon which has also been observed by Holtcr- 

 mann ^ in cultures of Polyporus bogoriensis. 



Kniep ^ observed that while a young basidium on the gills of a 

 normal fruit-body of Armillaria mellea contains two nuclei, a young 

 basidium arising directly on a mycelium of monosporous origin 

 contains only one nucleus. This difference may be readily explained 

 if we assume that A. mellea, like A. mucida,^ is heterothallic. In 

 all probability, in nature, each mycelium which gives rise to a fruit- 

 body arises from the union of two monosporous mycelia of opposite 

 sex. Hence the mycelium comes to have two nuclei in each cell 

 and, ultimately, the fruit-body two nuclei in each young basidium. 

 On the other hand, a mycelium grown from a single spore is neces- 

 sarily unisexual (haploid) and therefore has but one nucleus in each 

 young basidium produced directly upon the aerial hyphae. Experi- 

 ment with other heterothallic Hymenomycetes, e.g. Coprinus fime- 

 tarius, C. lagopus, Collyhia relutipes, and Schizophyllum commune, 

 has shown that, while a secondary (diploid) mycelium produced by 

 the fusion of two primary (haploid) mycelia of opposite sex pro- 

 duces fruit-bodies of normal appearance and vigour, single primary 

 mycelia remain quite sterile, or produce imperfect fruit-bodies, or 

 produce fruit-bodies of normal form onl}'^ occasionally and usually 

 after a much longer time than secondary mycelia.^ In Armillaria 

 mellea the secondary mycelia produce large fruit-bodies with stipes, 



^ C. Holtermann, Mycologische Untersuchungen aus den Tropen, Berlin, 1908, 

 pp. 94-95, Taf. IX, Fig. 8. 



2 H. Kniep, loc. ciL, Taf. III. 



^ H. Kiiiep, " tjber morphologische und physiologische Gesclilechtsditfer- 

 onzierung," Verhandlung der Physikal.-tned. Gesellschnft Z7i Wiirzburg, 1919, 

 pp. 12-i;3. 



* Mile Bensaude asserts that monosporous mycelia of Coprinus fimetarius are 

 completely sterile. Miss Mounce and W. F. Hanna, in my laboratory, have observed 

 that, while monosporous mycelia of C. lagopus always produce fruit-bodies, these 

 fruit-bodies have white or whitish gills and produce relatively few spores or no 

 spores at all. When spores are produced they are not shot from their sterigmata. 

 Miss Dorothy Newton, another worker in my laboratory, observed that of several 

 monosporous mycelia of Collyhia velutipes only one produced a fruit-body. The 

 fruit-body had a normal appearance but its spores would not germinate. Miss E. M. 

 Wakefield and Hans Kniep have observed that monosporous mycelia of Schizo- 

 phyllum commune are usually, although not always, quite sterile. For references to 

 the papers of Bensaude, Kniep, and Mounce, vide these Researches, vol. ii, 1922, 

 p. 395. 



