PLUS AND MINUS STRAINS IN THE GENUS GLOMERELLA 245 
Strain was present or was necessary for the development of the peri- 
thecial stage. Frequently cultures made from single spores would 
produce the perithecia, this seeming to prove that the species were 
homothallic, that is, with both sexual organs on the same strain. 
But during the past four years, several fungi of this group have been 
found which develop two strains which behave in some ways similar 
to the strains of the Mucorineae. There is a fertilization between 
them followed by the development of an abundance of perithecia 
where they grow together on culture media (plate I, fig. 2). While the 
behavior of these strains is not identical in all ways with the strains 
of the black molds, it seems best for lack of better terms to use here 
also the indefinite terms, plus and minus. 
While working on this problem, cultures from several different 
host plants have been obtained which have shown the presence of the 
two different sexual strains. The first one that was studied was 
obtained in northern Louisiana in August, 1910 from the petiole of a 
leaf of the cottonwood {Populus deltoides) . This one has been studied 
for nearly four years. A preliminary report^ on this was given at the 
Washington meeting of the Botanical Society of America in December, 
19I1. This fungus is a typical Gloeosporium and, from a micro- 
scopical examination, it is impossible to tell it from Gloeosporium 
fructigenum, the common form causing the bitter rot disease of apples 
{Malus sylvestris) . Other hosts from which the two strains have been 
obtained are the giant beggar weed {Desmodium tortuosum), okra 
{Hibiscus esculentus) , and morning glory (Ipomoea purpurea) . Most of 
the work discussed in this article was carried on with the two forms 
from cottonwood and morning glory. The cottonwood fungus has 
been kept in culture for nearly four years and is still producing peri- 
thecia in abundance when the two strains are together, and at no time 
has it shown any signs of deterioration or running out. 
The morning glory fungus is also interesting in another way from 
the fact that only perithecia develop in cultures. While conidia are 
usually very abundant in Glomerella cultures, none of these have ever 
been observed in either strain of the anthracnose collected from the 
morning glory. This is similar to the ascogenous culture from bean 
{Phaseohcs vulgaris) which Shear and Wood^ have reported. There 
^ Edgerton, C. W. Plus and Minus Strains in an Ascomycete. (Abstract) 
Science, n. s., 35: 151. 1912. 
2 Shear, C. L., and Wood, Anna K. Studies of Fungous Parasites Belonging 
to the Genus Glomerella. Bur. PI. Ind. Bui. 252: 46-47. 1913. 
