188 BOTANICAL GAZETTE [OCTOBER 
from zygosporic material which Namystowsk! kindly sent to one 
of us. NamySsLowskI (18), however, still believes, upon evidence 
which we have criticized, that heterothallic species have been 
shown capable of producing homothallic zygospores. 
The two examples given are typical of less careful observations. 
Although cases of homothallism in heterothallic species on a priori 
grounds were to be expected, we have never found them ourselves, 
and could not feel that the reports of them by other investigators 
could stand critical examination. It reminded one of the reports 
of the birth of a full black negro baby from pure white parents 
which from time to time have appeared in literature and been 
passed on by rumor, but which have in no case been confirmed 
by students of human heredity. 
BURGER ON CUNNINGHAMELLA 
The condition outlined was the situation in the early part of 
1919, when BURGER announced the finding of hermaphroditic as 
well as “pseudo-heterothallic’’ strains in Cunninghamella and 
Syncephalastrum. At the same time report came from one of the 
laboratories of the Department of Agriculture of a strain of Rhizopus 
which would form zygospores with both plus and minus test strains 
of this species. As to the Rhizopus, it was found upon inquiry that 
this particular strain had died out, and that after all it had not shown 
the capacity of conjugating with both the opposite sexes. BURGER’S 
paper on sexuality in Cunninghamella (14) presents the most exten- 
sive evidence which has yet appeared for sex intergrades in any 
heterothallic mucors. Although his arguments from the data pre- 
sented seemed open to some criticism, his publication made the genus 
Cunninghamella the most likely source known for sex intergrades, the 
investigation of which would have considerable genetic interest. — 
Recently published studies by one of us (11) had shown that races 
with plus and races with minus tendencies can arise by mutation 
from a homothallic species, and that such a race may cease to form 
zygospores and take on the appearance of a heterothallic species. 
It seemed worth while, therefore, to look for races with homothallic 
tendencies among heterothallic species, in view of BuURGER’s paper. 
Accordingly, a rather extensive study of the interaction of strains 
