3 <S RESEARCHES ON FUNGI 



and Ustilaginales, 1 suggests that these structures assist the mycelium 

 in some way in its physiological activities. 



It has been supposed that clamp-connexions in Hymenomycetes 

 and Gastromycetes have some sexual significance, but there does 

 not seem to be any evidence of weight in favour of this view. It is 

 true that the formation of the twin cross- walls of a clamp-connexion 

 is preceded by conjugate nuclear division. Yet this does not indicate 

 that the formation of clamp-connexions is a necessary accompani- 

 ment of conjugate nuclear division ; for (1) in Psalliota campestris, 2 

 Coprinus curtus, 3 Hypochnus solani {Rhizoctonia solani), 4 and certain 

 other Hymenomycetes, conjugate nuclear division goes on in the 

 diploid mycelium without any clamp-connexions being constructed ; 

 and (2) in the pilei of many Agaricaceae, even in species in which the 

 diploid mycelium produces clamp-connexions, e.g. Coprinus lagopus 5 

 and Clitocybe expallens, 6 clamp-connexions are not formed when the 

 nuclei divide conjugately. Moreover, in the Uredineae, in which 

 numerous conjugate nuclear divisions take place during the produc- 



I have found numerous clamp-connexions in the mycelium attached to the base of 

 the stipe. This new fact affords one more piece of evidence that P. pistillaris is 

 a true Basidiomycete, and it also indicates that the genus Podaxis is not closely 

 related to any known genera of Ascomycetes. 



1 Clamp-connexions occur in Ustilago, Doassansia, Urocystis, Tilletia, and 

 Entyloma, and they develop by means of a backwardly-growing hook, just as in the 

 Hymenomycetes. Vide R. Seyfert, " Uber Schnallenbildung in Paarmyzel der 

 Brandpilze," Zeitschrift f. Botanik, Bd. XIX, 1927, pp. 577-601. 



2 Max Hirmer, " Zur Kenntnis der Vielkernigkeit der Autobasidiomyceten. I.," 

 Zeitschrift f. Botanik, Vol. XII, 1920, pp. 657-674. 



3 H. Brunswik, " Untersuchungen liber die Geschlechts- und Kernverhaltnisse 

 bei der Hymenomyceten Gattung Coprinus,'''' in Goebel's Botanische Abhandlungen, 

 Heft V, 1924, pp. 124-125, 142. 



4 K. O. Miiller, " Untersuchungen zur Entwicklungsgeschichte und Biologie von 

 Hypochnus solani {Rhizoctonia solani),'" Arbeiten aus der Biologischen Beichsanstalt fiir 

 Land- und Forstmrtscha.fi, Bd. XIII, 1924, pp. 208-222. 



5 My own observations. 



6 Hans Kniep, " Uber die Bedingungen der Schnallenbildung bei den Basi- 

 diomyzeten," Flora, Bd. XI, 1918, p. 380. Kniep distinguished three groups of 

 these fungi : (1) those with clamp-connexions in all stages of development of the 

 diploid mycelium and of the fruit-body, and with a clamp -connexion at each cross- 

 wall ; (2) those in which clamp-connexions are completely absent ; and (3) those in 

 which clamp-connexions occur more or less irregularly. He also found that, in 

 certain species, but by no means all, when a diploid clamp-bearing mycelium is 

 submerged in a culture medium, it ceases to produce clamp-connexions. 



