L82 Report of the Department of Botany ok the 



THE EXPERIMENTS. 



The writer has sought to solve the problem by greenhouse experi- 

 ments which will now be described: 



Experiment No. 1. In the autumn of 1910 ten wooden boxes of 

 1350 cubic inches capacity were partially filled with soil from a field 

 in which a large portion of the potato crop of that season had been 

 destroyed by Phytophthora rot. Twelve large partially-decayed 

 tubers and a quantity of blighted potato stems cut into short sec- 

 tions were then placed in each box and the filling of the boxes com- 

 pleted by adding more of the soil. The boxes were left in the field 

 exposed to the weather until January 20, 1911, when they were 

 placed in a greenhouse. Tubers for planting in the boxes were 

 obtained from eastern Long Island, where potatoes were not affected 

 by Phytophthora in 1910. Previous to planting, the tubers were 

 washed, carefully examined for blemishes and given the formaldehyde 

 scab treatment. In each box the decaying tubers were broken into 

 pieces, which were thoroughly mixed with the soil. Eight of the 

 boxes were planted February 1, while the other two were reserved 

 for making soil filtrate for inoculation. From this time until the 

 plants were nearly full-grown the soil in the boxes was kept con- 

 stantly wet by watering nearly every day. On March 22 the plants 

 were 10 to 12 inches high, bushy and very thrifty. On this date 

 the largest and thriftiest of the plants was placed in a large glass 

 inoculation chamber in which the air was kept constantly at or near 

 the point of saturation by frequent watering. The leaves were wet 

 most of the time. The plant grew rapidly. By March 31 several 

 of the lower leaves had turned yellow, as they do in the field when 

 the weather is wet and the vines large. On April 19 some of the 

 younger leaves showed an cedematous eruption on the upper surface 

 along the midrib and larger veins. The conditions must have been 

 ideal for Phytophthora, yet none appeared up to April 25, when the 

 plant was removed from the inoculation chamber and another one 

 put in its place. 



The new plant had several stalks about 18 inches high and its 

 foliage was nearly perfect. It was heavily watered at noon on 

 April 25, and at 2: 30 p. m. of the same day its foliage was sprinkled 

 thoroughly with a soil filtrate prepared by stirring up a quantity of 

 the potato soil with water and filtering through cheesecloth. The 

 soil used contained the remains of decayed potatoes and potato stems. 



