PLUS AND MINUS STRAINS IN THE GENUS GLOMERELLA 
C. W. Edgerton 
With one figure in text and plates XXII and XXIII. 
Certain species of the Mucorineae, or black mold group of fungi, 
are composed of two distinct strains, either of which is capable of 
living by itself and of producing asexual spores, but neither is able 
alone to produce the zygospores or sexual stage. When the two strains 
are together, however, and the environment is suitable, the sexual 
spores are produced abundantly. In the formation of the zygospores, 
one gamete is produced by one strain and the other gamete by the 
other strain. In this group of fungi, the strains are very similar; in 
most cases it being impossible to differentiate between them from a 
macroscopic or microscopic examination. While these two are with- 
out doubt sexual strains, their similarity has made it seem advisable 
to Blakeslee, who has made a study of many of the forms, to use the 
indefinite terms, plus and minus, in preference to male and female 
Outside of the Mucorineae sexual strains in fungi are either very 
rare or else have not been recognized and it would seem that they are 
very rare as many unsuccessful attempts have been made to find them. 
However in the genus Glomerella, which is the perithecial stage of 
certain species in the form genera, Gloeosporium and Colletotrichum, 
a condition exists which approaches that found in the Mucorineae. 
The ascogenous stages of many of the Gloeosporiums and CoUeto- 
trichums have been known for a number of years. In some of the 
forms, as for example the one causing the bitter rot disease of apples, 
the perithecial stage is rather common, while in others its development 
seems to be rare. Yet with all of the forms the perithecia develop 
very erratically sometimes present in abundance and other times 
entirely absent. While working on these fungi during the past several 
years and trying to find out some of the reasons of the erratic develop- 
ment of the perithecia, the writer has constantly had in mind the 
possibility of sexual strains. Until about three or four years ago, 
nothing developed which would in the least show that more than one 
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