ANTHRACNOSE OF CUCURBITS. 



41 



previous test, only negative results were obtained. Owing to the 

 ravages of mosaic, field 2 was becoming unsuitable for work on 

 anthracnose and field 1 offered better possibilities. 



Table IV. — Anthracnose dissemination test by spraying potted cucumber plants with 

 drainage water from water traps. 



Trap. 



No. 1. 



No. 2. 



Serial num- 

 bers of pots 

 sprayed on 

 Sept. 5. 



139 

 148 



145 



146 



Number of 



anthracnose 



lesions on 



Sept. 14. 



None. 



None. 

 2 

 1 



Trap. 



No. 3. 

 No. 4. 



Serial num- Number of 



bers of pots [anthracnose 



spraved on lesions on 



Sept. 5. Sept. 14. 



136 

 137 

 140 

 -138 



5 



None. 

 7 

 6 



On September 12 four water traps (5, 6, 7, and 8), similar to those 

 in field 2, were placed in field 1 along the extreme western edge and 

 at the foot of the slope. The location of these is shown in figure 14. 

 The same day a rain of 0.66 inch occurred and the contents of these 

 traps were collected immediately afterwards. 1 Using the method 

 outlined above, dilutions were made from three of the samples and 

 a series of seven plates poured in each case. No anthracnose colonies 

 appeared in the plates from traps 5 and 7, but in the series from 

 trap 6 two colonies of the anthracnose fungus appeared. According 

 to the dilution used, this result indicates a spore content of 916 per 

 c. c. in the water in trap 6. 



The liquid collected from these traps was also sprinkled on healthy 

 potted plants in the greenhouse. 1 Seven pots were thus inoculated, 

 and on September 19 the plants in each pot were diseased. Each 

 sample produced anthracnose infection, and it is quite evident that 

 spores were present in the drainage water caught in each trap. It 

 is also apparent that this method is superior to the poured-plate 

 method for detecting the presence of the spores in such an inoculum. 



These experimental tests prove conclusively that which the ob- 

 servational evidence indicated, namely, that the spores are carried 

 through the fields by surface drainage water during rains. As to 

 the distance carried, recovery of the fungus from these traps along 

 the edge of the field indicates that the spores were transported at 

 least as far as the extremities of the field in question, and there is 

 no reason to suppose that they might not be carried much farther. 

 However, the main importance attached to this agency is that it 

 serves to disperse the fungus far and wide through the particular 

 field already containing original centers of infection. 



Water, then, is not only necessary for the germination of the spores, 

 but is also essential to the separation of the spores from the lesion. 

 In the shape of rain, it washes the spores to the soil and spatters 

 them on to the host plants. In the shape of surface run-off, it dis- 



i These traps were placed and the contents collected by Dr. E. Carsner. 



