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VOLUME LXXII NUMBER 4 
tHE 
DOTANICAL GAZES 
OCTOBER 1921 
SEXUAL DIMORPHISM IN CUNNINGHAMELLA 
ALBERT F. BLAKESLEE, J. LINCOLN CARTLEDGE, AND 
DoNnaALtpD S. WELCH 
(WITH ONE FIGURE) 
Introduction 
HETEROTHALLIC AND HOMOTHALLIC FORMS 
In 1904 (1) it was shown that the mucors can be classified into 
two main groups according to their ability to produce zygospores 
from the sowing of a single spore. Species which are able to form 
sexual spores by the conjugation of branches from the same plant 
were called homothallic, since the mycelia appeared to be sexually 
alike; those which were able to form sexual spores only by the 
interaction of different plants were called heterothallic, since the 
mycelia taking part in conjugation appeared to be sexually different. 
The terms homothallic and heterothallic were used instead of 
hermaphroditic and dioecious because at the time they were first 
Suggested our knowledge of sexuality in the mucors did not seem 
to warrant unreservedly accepting the idea of a strict sexual 
dimorphism in these forms, although such a dimorphism was 
strongly indicated by the interaction which had just been dis- 
covered between plus and minus races. 
In later publications (5, 6) the desirability was pointed out of 
extending the use of the terms homothallic and heterothallic to 
signify the type of sexual differentiation in all gametophytes, in 
contrast with the terms homophytic and heterophytic suggested 
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