194 BOTANICAL GAZETTE [OCTOBER 
combination pairs capable of reacting with both plus and minus 
races. If all of the 325 possible contrasts had been made between 
the twenty-six races instead of only the 135 actually attempted, 
it is probable that a considerably larger number of pairs of races, 
capable when mixed of producing zygospores with both plus and 
minus races, would be evident. So far as the data of BURGER go, 
however, they are sufficient to show that absence of zygospores in 
a culture cannot be offered as proof that it is not a mixture of 
strains; and to indicate that infection, if it occurred, rather than 
the existence of pseudoheterothallic hermaphrodites, might be the 
cause of zygospores in cultures where they would not be expected 
on the basis of sexual dimorphism. 
BuRGER believed he had eliminated the possible objection that 
his cultures had been mixed by making several single spore cultures 
from each of the strains nos. 9, 3, and 21, and obtaining zygospores 
whenever such cultures from one of these strains were contrasted 
with those from either of the other two strains. The test, on the 
face of it, may appear to be a critical one, and in fact if only these 
three strains had been kept in cultivation they would now afford 
an opportunity of critically retesting data upon which BURGER’S 
theories are based. Since, however, these cultures were destroyed 
before the publication of his paper in which their peculiar behavior 
is described, it will be necessary to depend upon circumstantial 
rather than upon direct evidence. As seen from table I, nos. 9 
and 3 may be considered good plus and minus races, and in conse- 
quence should be expected to give reactions when grown together. 
In consequence, interest centers rather in strain no. 21. This race 
it will be remembered gave the most aberrant reactions, and 
together with nos. 14 and 20 is able to account for all the evidence 
that can be brought forward in support of BuRGER’s theory 0 
pseudoheterothallism. No 21 is predominantly minus and so 
should be expected to give reactions with the plus strain no. 9. 
The abnormal reaction, therefore, is between nos. 21 and 3. The 
surprising thing about these tests is that apparently there were no 
controls. Each of the three single spore cultures of no. 3 were 
contrasted against each of the four single spore cultures of no. 21, 
