PLUS AND MINUS STRAINS IN THE GENUS GLOMERELLA 247 
or bean agar, the perithecia of the forms studied do not mature; they 
remain small and no asci develop in them. On some special medium 
such as Clinton's oat juice agar^ which has been acidified, some of the 
perithecia come to maturity, but, even on this medium, the asci are 
usually irregular in shape (fig. la) and do not seem to have developed 
properly. 
Most of the work in the past on perithecial forms of the genus 
Glomerella seems to have been done with what is called the plus 
strain in this article. The description of the genus Glomerella as 
given by Spaulding and von Schrenk^ was based on the characters of 
Fig. I. Asci from the cottonwood Glomerella as formed on oat juice agar: 
a, Asci from the minus strain; b, Asci from the plus strain; c. Asci from the boun- 
dary line between the two strains. 
the plus strain of the fungus that causes the bitter rot disease of apples. 
The cultures with ascogenous stages used by Miss Stoneman,^ Clinton,^ 
Sheldon,^ and a few others were apparently all of this strain. Yet 
there are a few cases in the published literature where it seems almost 
^ Clinton, G. P. Oospores of Potato Blight. Conn. Agr. Exp. Sta. Report 
1909-1910: 760-761. 191 1. 
* Von Schrenk, Hermann, and Spaulding, Perley. The Bitter Rot Fungus. 
Science, n. s., 17: 750-751. 1903. 
^ Stoneman, Bertha. A Comparative Study of the Development of Some 
Anthracnoses. Bot. Gaz. 26: 69-120. 1898. 
^ Clinton, G. P. Apple Rots in Illinois. 111. Exp. Sta. Bui. 69. 1902. 
Sheldon, J. L, The Ripe Rot or Mummy Disease of Guavas. West Va. 
Exp. Sta. Bui. 104. 1906. 
