Oct. ii, 1915 
Phytophthora infesians in Irish Potato 
85 
hills in the four check rows were watched as carefully as those in the 
two rows planted with infected seed, but no infections with P. infestans 
were found. 
The development of foliage infection from the three centers described 
was gradual and wholly comparable to that described in considerable 
detail in the studies of 1913. It should probably be said in this con¬ 
nection that the first foliage infection was found on July 27, five days 
after the first case was discovered. By August 14 leaves within a radius 
of 10 to 20 feet from each center or station were infected with P. infes¬ 
tans. A bad epidemic of late-blight was in full swing throughout the 
whole 2-acre field by September 10. It is plain that the three centers 
above described formed the starting points for this epidemic. Other 
centers of infection may have developed subsequently, but no attempt 
was made to follow the later developments because of the constant 
recurrence of new foliage infections resulting from the infections about 
the original centers. The results of the field studies of 1914 confirmed 
in every way the results obtained in 1913. 
The fact that a tuber infected with late-blight may cause an epidemic 
of the* disease raises the question as to the r 61 e of infected tubers left in 
the field at harvest time. The majority of these are killed by frost, 
but a few remain in the soil or get covered during the digging of the 
crop and may pass through the winter in a living condition. Observa¬ 
tions showed plainly that many tubers survived the winter of 1913 in 
Aroostook County, Me. The fields planted to oats in 1914 that had been 
in potatoes the previous season were well sprinkled with volunteer 
potato plants. It is common knowledge among the growers of northern 
Maine that some seasons volunteer potato plants are very plentiful. 
Their presence or absence is determined largely by the season, especially 
by the time and amount of snowfall. 
POSSIBILITY OF CONIDIA OF PHYTOPHTHORA INFESTANS BORNE ON THE 
SEED TUBER REACHING THE SURFACE AND CAUSING FOLIAGE IN¬ 
FECTION 
In 1876 De Bary (4) called attention to the possibility of conidia on 
the seed tuber being able to reach the surface and cause foliage infection. 
Hecke (12) and Clinton (8) are inclined to believe they function more 
extensively than the mycelium in the seed tuber. Little is known about 
the production of conidia on infected potato tissue in the soil or their 
relation to renewing infection from one year to another. For this reason 
it was thought advisable to learn something about the possibility of the 
fungus fruiting on cut seed in the soil and whether the spores functioned. 
To this end 31 infected seed pieces were planted in the usual manner 
on June 22, 1913, at Houlton, Me. The soil was quite dry, and the soil 
temperature ranged from io° to 14 0 C. Three days later they were dug 
