1921] BLAKESLEE, CARTLEDGE, & WELCH—CUNNINGHAMELLA 187 
drawings were made the homothallic strand was lost in an attempt 
to make a permanent mount of the fresh material. So far as we are 
aware, such a condition as Miss McCormick figures has not been 
described elsewhere for Rhizopus since 1903, when heterothallism 
was first discovered in the mucors. Inasmuch as an enormous 
number of zygospores of Rhizopus must have been observed more 
or less closely during this time, since it is a common type for labora- 
tory study (Miss McCormick herself [16] reports having examined 
over 2000 in her cytological investigations in this species), it appears 
reasonable that in an isolated instance of this kind, the filaments 
from the two sides of the zygospore which appeared to be connected 
may in fact have been separate, but the place of separation obscured 
by overlying hyphae. That it is unsafe to judge of the thallic 
condition of a species from the hyphal connections is shown by 
experience with a class of students who were studying Rhizopus 
shortly after heterothallism had been discovered in other mucors, 
but before it had been demonstrated for this species. They were 
asked to find cases in which both the suspensors originated from 
branches of the same filament. A number of cases were found in 
which the two suspensors actually seemed to be connected, but in 
every instance there were one or more overlying filaments which 
would render the condition open to doubt by a critical observer. 
The second case is a paper by NAMYsLowskKI (17), in which he 
throws doubts upon heterothallism in the whole group of the mucors. 
His experimental evidence comes from isolating single spores of 
Rhizopus and sowing the resulting mycelia on bread. The appear- 
ance of zygospores in fourteen out of forty-six such single spore 
cultures led him to conclude that his Rhizopus was homothallic. 
As has already been pointed out (7), the facts that six of these 
cultures were destroyed by bacteria and that thirteen more were 
devoid of even sporangia and hence probably also infected with 
bacteria, rendered it probable, to one familiar with pure culture 
methods, that the zygospores which NamysLowski obtained in 
part of his cultures from the sowing of a single spore actually might 
have arisen through interaction with the opposite sex which had 
gained access to these cultures through infection. This explanation 
seemed later confirmed by the isolation of the two sexual strains 
