Mar. 2s. 1915 Dissemination of Chestnut-Blight Fungus 495 



the ground without being carried any appreciable distance is not men- 

 tioned. Since they germinate at once in rain water, the great bulk of 

 such spores would be lost for anything but ver}' local infections. The 

 really important point would appear to be the length of time shooting 

 continues after a rain ceases, for at that time the conditions of the atmos- 

 phere would be such as to favor a \\'ider dissemination. This question 

 does not seem to have been satisfactorily answered. The data given on 

 height and horizontal distance of projection, as well as the rate of expul- 

 sion, certainly indicate the importance of wind transport of spores 

 following rainy periods. 



The spore content of the air was studied b}' means of aspirator tests 

 and exposure plates. In this work, carried out during drj' weather, 

 Anderson and his assistants failed to get positive results under natural 

 conditions in the field. They report the use of over 100 exposure plates 

 and tests of 500 liters of air without finding a single spore of the chestnut- 

 blight fungus. Tests made of aspirated air and by exposure plates gave 

 positive results, however, when the cankers were artificially drenched 

 ■with water. For the aspirator tests the horizontal distances of the 

 aspirator opening from the canker varied from 2 inches to 5 feet (?) and 

 the maximum vertical distance was 22 feet. 



The tests made by exposing agar plates under artificial conditions in 

 the field again pointed to the probability of wind dissemination, but one 

 is forced to admit that they were not conclusive, since the conditions 

 were so different from the natural in that the cankers were drenched 

 with water artificially instead of waiting for a rain. The results with 

 exposure plates may be summed up as follows: No spores of the chestnut- 

 blight fungus were obtained under natural conditions in the field during 

 dry weather; by the use of artificially drenched cankers spores were 

 obtained at distances varying from i inch to 51 feet, with very few at 

 the maximum distance. 



The final and most conclusive argument in favor of wind dissemination 

 in the minds of the authors cited was afforded by inoculations made by 

 offering an opportunity for wind-borne spores to be introduced into 

 wounds. There is little doubt in the minds of the writers of this paper 

 that infection did take place in the way claimed, but it should be pointed 

 out that a covering of cotton would not prevent spores from being washed 

 into the wounds by rains (6). A fairly compact mass of cotton has been 

 shown to retain but few of the pycnospores present in water passing 

 through it. It must therefore be admitted that, under the conditions 

 of the experiments reported, infection by spores washed down by rains 

 was one of the possibilities. 



It is interesting to note in this connection lliat Kittredge (10), as a 

 result of field observations on the spread of the disease around a center 

 of infection, arrives at the following conclusion: 



The location of infected trees in partially infected groups of sprouts shows that 

 wind is not the prime factor in the distribution of the spores. 



