Homothallism and Heterothallism in Coprinus. Irene Mounce. 257 
obtained by Mlle Bensaude and Hans Kniep; certain pairs of 
mycelia produced clamp-connections in large numbers and 
others never produced any clamp-connections at all. Moreover, 
the pairs of mycelia which produced clamp-connections gave 
rise to perfect fruit-bodies, whilst those pairs which did not 
produce clamp-connections gave rise only to imperfect fruit- 
bodies. I therefore came to the conclusion that the strains of 
Coprinus lagopus used for my new investigation were hetero- 
thallic. It then seemed highly desirable that I should re- 
investigate the mycelia of Coprinus sterquilinus, C. stercorarius 
and C. niveus. I therefore made a new series of cultures for each 
of these species. With Coprinus sterquilinus and C. stercorarius, 
I obtained results exactly similar to those already recorded: 
clamp-connections appeared regularly on all the mycelia of 
monosporous origin. My conclusion that these two species are 
homothallic was therefore confirmed and strengthened. With 
Coprinus niveus, just as with C. lagopus, I found that in a 
_ series of monosporous cultures not a single mycelium gave rise 
to clamp-connections but that, on pairing the mycelia, some- 
pairs produced clamp-connections abundantly and some pairs 
no clamp-connections whatever. I have therefore convinced 
myself that the strain of Coprinus niveus used for my new 
investigation is heterothallic. 
The object of this paper is to bring forward further evidence 
in support of my previous conclusion that Coprinus sterquilinus 
and C. stercorarius are homothallic and to show that Coprinus 
lagopus and C. niveus are not always homothallic, as I at first 
believed, but are often, and perhaps as a rule, heterothallic*. 
II. CRITERIA OF SEX. 
This paper is to be regarded as a continuation of the one 
already published. Here, therefore, it will not be necessary to 
discuss the criteria for distinguishing a homothallic species of 
Coprinus from a heterothallic one in detail; and it will be 
sufficient for our present purpose to remind the reader of the 
following facts. Mlle Bensaude and Hans Kniep, working inde- 
pendently, have shown that the presence of clamp-connections 
on a mycelium is associated with dicaryons and the conjugate 
division of the nuclei. Clamp-connections, therefore, are an 
outward and visible sign that the mycelium on which they arise 
is in the diploid and not the haploid condition. A species of 
Coprinus producing clamp-connections is homothallic if clamp- 
* These results were communicated to the Mycological Section of the 
American Botanical Society at the Toronto meeting of the American Associa- 
tion for the Advancement of Science, December, 1921, in a paper entitled: 
“Homothallism and Heterothallism in the Genus Coprinus’”’; but no abstract 
of this paper has been published. 
