96 
Journal of Agricultural Research 
Vol. V, No. a 
This method of perpetuation readily explains how P. infestans has 
spread from its native home in South America to every corner of the globe. 
As pointed out by Jensen (14), it was probably brought to Europe in the 
mycelial stage in seed potatoes. Likewise, it may well have gone to 
Australia, New Zealand, North America, and other parts of the world. 
MYCELIUM OF PHYTOPHTHORA INFESTANS IN THE SOIL 
That the mycelium might live over winter in the soil was possibly first 
suggested by Kuhn (18), who arrived at this assumption because he was 
unable to grow infected plants from diseased tubers, combined with the 
fact that the potato fungus occurred year after year. This theory 
received support later at the hands of Brefeld (7) in connection with his 
excellent cultural studies of the smuts. He devoted some attention to 
P. infestans also and was probably the first to grow this fungus sapro- 
phytically in semipure cultures. It was this significant achievement that 
led him to support Kuhn's theory. 
Darnell-Smith (10) has studied the possibility of P. infestans living 
over in the soil. A large number of experiments were made by mincing 
infected tubers in the soil and planting it to potatoes. He also smeared 
spores on the tubers when planted, but in no case did he get any infection 
of P. infestans. Some recent experiments by Stewart (33) also bear 
directly on Brefeld’s theory (7, p. 26). He planted healthy tubers in soil 
mixed with blighted vines and tubers and made conditions highly favor¬ 
able for the infection of the growing potato plants. No infection of 
P. infestans was obtained. 
According to the writer’s studies, under certain conditions of moisture 
and temperature the fungus may grow and sporulate on the surface of 
the soil to a very limited extent, as described in an earlier part of this 
paper, but no evidence was obtained showing that it remains alive in the 
soil for extended periods of time. Jones, Giddings, and Lutman (17) 
have also recorded the fact that the fungus may spread from infected 
tissue out over the surface of the soil to a limited extent. Our increased 
knowledge of culturing parasitic fungi on artificial media, and especially 
of P. infestans , does not permit such deductions at the present time as 
were made earlier by Brefeld (7). 
MASSEE’S LATENT-MYCELIUM THEORY 
The early literature on P. infestans , then known as the “ potato mur¬ 
rain,” is full of interesting theories as to its origin. The literature is in 
every case naturally tinted with spontaneous generation and lack of infor¬ 
mation as to the life history of the fungus. Fully as interesting is a theory 
more recently advanced by Massee (20). He maintains that the usual 
explanation for the sudden appearance of P. infestans over wide areas 
by the dissemination of conidia is inadequate and that the fungus is 
