248 
C. W. EDGERTON 
certain that the minus strain was also used. In a previous article, 
the writer^ described a culture from apple which no doubt belonged to 
this stage. This culture was explained at the time as a possible 
mutation but from the observations of the past few years, there seems 
no doubt but what this was really the minus strain of the bitter rot 
fungus. Shear^ also seems to have had both strains of several of the 
forms on which he has been working though he did not consider them 
to be sexual strains. 
When plantings of the plus and minus strains were made short 
distances apart on nutrient media in petri dishes and the two develop- 
ing colonies allowed to grow together, the probability of them being 
sexual strains became evident. Up to the time the colonies came in 
contact, the growth of each was similar to that described above. On 
the boundary line, however, where they were in contact, there de- 
veloped a black line of perithecia (Plate I, fig. 2). Under suitable 
temperature and cultural conditions these perithecia from the boundary 
were mature and shedding their ascospores in four or five days after 
the strains joined, while the development of the asci in a single strain 
alone was always much slower. On practically all media tried, espe- 
cially when acidified, this black line of perithecia developed. On bean 
agar (Plate I, figs. 2 and 3; Plate II, fig. i) on which the minus strain 
produced only immature perithecia, the boundary line was black with 
perithecia with well-developed asci. On oat juice agar (Plate II, fig. 
2) on which the minus strain produced poorly formed asci, the boun- 
dary line was a ridge of perithecia sometimes more than a millimeter 
high with perfectly developed asci. In Plate I, figures 4 and 5, are 
shown photomicrographs of sections across the boundary line on oat 
juice agar. On the left side in each case is the minus strain, and on 
the right the plus strain. In the minus strain may be seen the small 
immature perithecia. Where the two strains come together, the 
perithecia are large and well developed and many of them extend up 
above the culture medium. In Plate I, figure 4, the perithecia on the 
boundary line are just forming and are still immature while those in 
figure 5 are well developed and filled with asci. Several hundred of 
such plate cultures have been made during the past four years and in 
^ Edgerton, C. W. The Physiology and Development of Some Anthracnoses. 
Bot. Gaz. 45: 395-396. 1908. 
^ Shear, C. L., and Wood, Anna K. Studies of Fungous Parasites Belonging to 
the Genus Glomerella. Bur. PI. Ind. Bui. 252. 1913. 
