SIX KINDS OF MYCELIA 203 



diploid phase. Microscopical exairtination of the mycelium for 

 presence or absence of clamp-connexions and for the mode of 

 branching constantly confirmed criterion No. 5, 



When two paired mycelia growing on dung-agar in a Petri dish 

 were being examined to determine the mode of branching and the 

 presence or absence of clamp-connexions, the Petri dish was usually 

 turned upside down on the stage of the microscope and the mycelium 

 was viewed with the low-power objective. Thus, the dish was not 

 opened, with the result that the mycelia were not subjected to 

 changed conditions of transpiration and, at the same time, the risk 

 of contamination of the medium was reduced to a minimum. Only 

 occasionally, for special or very critical observations, or when the 

 mycelia were not further required, the Petri dish was opened and 

 the mycelia were examined from above with the high-power 

 objective. 



The Four Kinds of Haploid and the Two Kinds of Diploid 

 Mycelia. — As determined by mating experiments,^ the monosporo\is 

 mycelia (each derived from a single basidiospore) of Coprinus 

 lagopus fall into four groups. If it be assumed that each mycelium 

 bears one of each of two pairs of sex factors Aa and Bb, then the 

 four groups of mycelia and the four groups of spores from which they 

 have been derived may be represented by the symbols : (AB), (ab), 

 (Ab), and {aB). 



Successful mating of the haploid mycelia of Coprinus lagopus 

 with the production of a diploid mycelium (bearing clamp-con- 

 nexions) is normally possible only in the combinations {AB) X {ab) 

 and (^6) X {aB), and therefore the fusion nucleus in every basidium 

 contains all the four sex factors and may be represented by the 

 symbols {AaBb). 



Since, as a rule, diploid mycelia in Coprinus lagopus can be pro- 

 duced only by the combinations {AB) x {ab) and {Ab) X {aB), but 

 not by the combinations {AB) X {Ab), {AB) x {aB), {ab) X {Ab), 

 or {ab) X {aB), we may assume with Kniep^ that like factors repel 

 one another while unlike factors attract one another. The mycelia 



1 W. F. Hanna, ""The Problem of Sex in Coprinus lagopus," Ice. cit. ; also 

 Dorothy E. Newton, " The Distribution of Spores of Diverse Sex, etc." loc. cit. 

 ^ Hans Kniep, "Die Sexualitat der niederen PHanzen," Jena, 1928, pp. l-M-l. 



