Homothallism and Heterothallism in Coprinus. Irene Mounce. 259 
from two dung-tubes, the procedure was the same, except for 
the fact that the two pieces of mycelium-covered dung were 
removed from the tubes by means of sterilised forceps instead 
of by a platinum loop. 
After portions of two monosporous mycelia had been de- 
posited near one another in an agar plate, the hyphae soon 
began to grow radially outwards through the agar; and, after 
a few days, the hyphae of the two mycelia came into contact 
in a line passing through the centre of the plate, so that fusions 
could take place between them. At the end of 7-14 days from 
pairing, the compound mycelium was examined under the high 
power of the microscope for the presence or absence of clamp- 
connections. 
In the heterothallicstrains of Coprinus lagopus and of C. niveus, 
a primary (haploid) mycelium differs from a secondary (diploid) 
mycelium in several ways. (1) A primary mycelium produces 
oidia in great abundance but asecondary does not. (2) A primary 
mycelium does not bear clamp-connections, whereas a secondary 
one does on all the stouter hyphae. (3) The branching of a 
primary mycelium is relatively irregular, whereas in a secondary 
mycelium it takes place on all the leading hyphae at a definite 
angle. (4) It was also noticed that in a primary mycelium the 
aerial hyphae are more abundant and, therefore, collectively, 
are more woolly in appearance than in a secondary mycelium. 
Owing to these differences between a primary and a secondary 
mycelium, one could usually tell macroscopically, 7-14 days 
after pairing, whether the sexes of any two paired mycelia were 
the same or different. Microscopic observation as to the presence 
or absence of clamp-connections, therefore, usually confirmed 
what had been surmised by examination with the naked eye. 
IV. COPRINUS STERQUILINUS, 
The series of monosporous cultures of Coprinus sterquilinus of 
which I gave an account in my first paper has been extended, 
and now fruit-bodies have been obtained from monosporous 
mycelia for seven successive generations. When grown under 
similar conditions, the mycelia of the seventh monosporous 
generation were found to fruit just as readily and as perfectly as 
compound mycelia derived from many spores of a wild fruit-body. 
Clamp-connections were found in the new cultures: (I) on 
each of two mycelia which originated from single spores pro- 
duced by a fruit-body of the sixth successive monosporous 
generation, and (2) on each of four mycelia which originated 
from single spores produced by a fruit-body of the seventh 
successive monosporous generation. These results are in com- 
plete accord with those given in my first paper. 
