84 Journal of Agricultural Research voi. v. no. 2 



the latter place. A plot of ground was selected that had been lying 

 idle in 191 3, but which before had grown several crops of potatoes in 

 succession. 



Tubers of the Green Mountain variety showing all stages of infection 

 by P. infesians were selected on May 25 from potatoes grown and held in 

 storage throughout the winter in potato cellars at Caribou. Most of 

 them were badly infected, as was natural to expect at this late date. 

 Many had only one living eye, while others, of course, had several. 

 Both whole and cut seed were planted in the same way as already de- 

 scribed in the field tests of 1913. In one row 170 whole tubers were 

 planted and 363 in two rows adjoining. On each side of these three 

 rows two rows were planted wath sound seed as checks, also of the Green 

 Mountain variety. The planting was made on June 2, when the soil 

 was drier than usual. There was very little rain until July 20, when an 

 inch fell, but, as a whole, the season was drier than that of 191 3 and 

 therefore was less favorable for the development of late-blight. 



An examination made on July 15 showed that 47.6 per cent of the 

 whole infected tubers, 37.4 per cent of the cut infected seed, and 92 per 

 cent of the healthy seed in the four adjoining rows came up. The low 

 percentage of germination of the infected seed was probably due to two 

 factors, the large amount of infection of the seed with P. infesians and 

 the dry weather following planting. The infected seed rotted in the 

 ground in the same way as described in the studies made in 1913. 



The first case of infection by this fungus was discovered on July 22, 

 two days after a heavy rain had fallen. It was in a hill grown from a 

 whole infected tuber having nine shoots from 12 to 18 inches tall. Five 

 of the smaller shoots were found to be infected at and below the surface 

 of the soil. The soil was carefully removed from about the hill, and two 

 of the five were found to be discolored all the way from the mother 

 tuber up to the surface of the soil. The three others seemed to have 

 become infected at the surface of the soil, probably by spores borne on 

 the two shoots most generally infected. The infection of neighboring 

 stems in the same hill above the surface of the soil was also noted in the 

 field studies of 1913. 



Two days later another hill, also grown from whole seed, was found to 

 be infected. This had 14 shoots, varying from 10 to 18 inches high. 

 The smallest shoot was discolored in the same way as described in the 

 previous case, and upon further investigation the infection was found 

 to extend down to the parent tuber. The fungous infection was evident 

 by the glistening white growth on the stem just above the surface of the 

 soil. None of the older shoots in this hill were infected at this date. 



On July 26 one of four shoots in a hill grown from cut seed was found 

 to be infected. These four shoots ranged from 6 to 14 inches in height. 

 Two of the smallest shoots in this hiU were infected with P. infesians. The 



