A Study of Meadow-Crop Diseases in New York 



67 



due to the higher temperatures. At any rate, it cannot be due to differ- 

 ences in length of day, because in the last experiment described the 

 length of daj- was the same in the greenhouse as on the window ledge. 

 Of course, the direct sunlight on the tubes in the greenhouse may have 

 inhibited spore production, although it did not inhibit the growth of 

 the fungus. 



It should be mentioned incidentally that the black color commonly 

 found in cultures of the fungus was practically absent from the fungus 

 in the tubes from which the light had been excluded. This agrees with 

 Miller's observation that light causes the darkening of ejected ascospores 

 (1925:226). 



Hopkins (1923 : 125) found perithecia on the dead overwintered leaves in 

 the spring which served as sources of inoculum. Miles (1925:678) finding 

 incipient perithecia on the seed believes that this explains distribution. 

 Miller (1925:226-230) germinated spores after they had lain a year under 

 dry conditions. He found that the asci absorbed water, became inflated, 

 burst the neck from the perithecium, and discharged spores as high as 10 

 centimeters toward the light. Spores germinate within twelve hours and 

 produce several tubes. These, according to Hopkins, penetrate the 

 cuticle directly (1923:126). 



Control 



Experiments with fungicides in the laboratory were limited because of 

 a paucity of spore material. Spore suspensions usually were too dilute 

 to be of great value even when the cultures could be induced to form 

 spores at all. The results of one experiment, however, appear in table 20. 



TABLE 20. 



Effect of Sulfur and Copper Dusts on Germination of Ascospores 



OF PSEUDOPLEA TrIFOLII 



Treatment 



Total 



number of 



spores 



Per cent of 

 germination 



I Ihecl 



7.2-per-cent copper-lime dust 

 3.6-per-cent copper-lime dust 



Kolodust 



200-mesh dusting sulfur 



Bank's colloidal sulfur dust. . 



172 

 215 

 80 

 89 

 62 

 56 



95.4 

 0.0 

 87.5 

 95.0 

 98.5 

 93.5 



The above experiment illustrates the general reaction of the fungus to 

 copper and sulfur dusts. The spores used came from pure cultures. The 

 fungus apparently is not sensitive to sulfur, so that further work with 

 t his protectant looking to field control is likely to be fruitless. Copper-lime 

 dust, however, might give control under field conditions. 



