A Study of Meadow-Crop Diseases in New York 



105 



agar, 8 cornmeal agar, and potato agar, were prepared and plates were 

 poured with 20 cubic centimeters of each. For each isolation triplicate 

 plates of each medium were inoculated as uniformly as possible in the 

 center with a piece of agar containing mycelium. All of the plates were 

 placed on a laboratory shelf under identical conditions. The diameter of 

 the thalli to the nearest millimeter was determined daily at the same hour, 

 by making two measurements at right angles to each other. Plates con- 

 taining occasional contaminations were discarded. Measuring the thalli 

 every day was unsatisfactory because of the marked daily variation under 

 the conditions of the experiment. 



The data are summarized in table 29. These same figures would have 

 been obtained by measuring the thalli at the end of the experiment instead 

 of daily. 



TABLE 29. Average Daily Increase in Diameter (in Millimeters) of Thalli of 

 Various Strains of Helminthosporium Vagans 



Culture no. 



The table indicates that 231, 232, 251, and 127, as well as 271 and 272, 

 may be placed in a group which grow at about the same rate. Isolation 

 128 might conceivably be placed in this group, but it grows uniformly 

 somewhat faster than do the others. Cultures 242 and 244 are in a 

 class by themselves and differ from each other in that 242 grows slightly 

 the faster. 



From observations of color reactions and general appearance made at 

 the conclusion of the experiment, the following cultures were grouped 

 together as probably representing a single physiologic form: 127, 231, 232, 

 251, 271, and 272. The color of this group by reflected light on potato 

 agar ranges from blackish green gray (Ridgway, 1912) to Sanford brown 

 in the center. There is a narrow apricot -orange margin which is sharply 

 defined. It will be recalled that these colors appear in the symptomatology 

 complex. On oat agar the aerial mycelium is somewhat more prominent 

 in the center, where it ranges from a blackish brown to an olivaceous black. 

 Oat agar appears If) be the best differential medium for the forms. On 

 cornmeal agar differences are not striking. The mycelium is much thin- 



' The media were prepared as follows: Coons', 10 cubic centimeters each of M/5 magnesium sulfate 

 plus 7 H2O, potassium acid phosphate, asparagin, and maltose, per liter; oat, 35 grams of 3-minute oat 

 flakes and 14 grams of agar per liter; cornmeal, 30 grams of Quaker cornmeal and 14 grams of agar per 

 liter; and potato, 210 grams of peeled potatoes and 18 grams of agar per liter. 



