231 
Oct. 3o f 1916 Spongospora subterranea and Phoma tuberosa 
for, as already stated, the land was uneven on account of the ridging, 
and plots 1 and 2 were at the edge of the orchard and had more sunlight 
and consequently gave a larger average yield per hill. 
The hill was considered a unit, each being harvested separately. The 
tubers were examined individually, being washed before examination 
if not clean when taken out of the soil, and a record made of the number 
of infected and the number of sound tubers in each hill and also of the 
gross weight of each. 
As shown by Table VI, some of the progeny of the checks planted 
with diseased seed gave from 42 to 68 per cent of infection, the varia¬ 
tion depending doubtless on the soil and water conditions in different 
parts of the field. 
In drawing conclusions from the results given in Table VI it must be 
borne in mind that in each case only a comparatively small number of 
hills were used and that variation in the soil and moisture contents 
materially influenced the results. Notwithstanding these facts, how¬ 
ever, it is perfectly obvious from the tests that several chemicals have 
a deleterious effect on the development of Spongospora subterranea , the 
most active being mercuric chlorid and formaldehyde, hot solutions being 
more effective than cold. 
During the season of 1915 the most promising of the experiments 
made in 1914 were duplicated, the land used being cleared in the spring 
and put in condition for planting. This land was much lower than that 
used in 1914 and not so well drained. The soil was a rather heavy gray 
silt with considerable humus at the surface. The soil of parts of this 
plot was of the type on which much of the infection in northern Maine 
occurs. The land was planted by hand on June 10, the seed being 
handled in the same way as that used in the experiment of 1914. The 
arrangement of the plots with regard to each other and the results 
obtained when harvested on October 10 are given in Table VII. 
The most striking result of this experiment is the infection of the 
control plots planted with healthy seed. One of these check plots was 
on each side of the field, which consisted of about one-fourth of an acre, 
and one in the middle, the former being numbered 1 and 9 and the latter, 
in which there were four rows, 18. Plots 1 and 9 received the same 
treatment as the plots used in the experiment in 1914, but plot 18 re¬ 
ceived special care in preparation and planting; moreover, the seed used 
in this plot was rigidly selected, inspected, and treated with double¬ 
strength mercuric chlorid. Everything with which it came in contact 
until planted was also disinfected with mercuric chlorid. 
