322 
Joumal of Agricultural Research 
Vol. XXX, No. 4 
as early as lighter types, planting is de¬ 
layed, so that the plants are younger 
and more readily destroyed when con¬ 
ditions favorable for the disease develop. 
This condition does not furnish an ade¬ 
quate explanation for the prompt 
appearance of the disease with intensive 
culture on this soil, however. An¬ 
other soil type upon which the disease 
develops with almost equal severity, 
though usually at a later stage in the 
development of the plant, is a very 
sandy soil in the trucking district south 
of Baltimore, Md. Although it is not 
obvious at first that there is any com¬ 
mon condition in these extreme soil 
types that causes them to be favorable 
for the development of the disease, 
nevertheless observation of conditions 
in these districts and in others which 
will be cited later has led to the conclu¬ 
sion that it is the retention of water in 
both soils for a long period after rains 
that furnishes the favorable environ¬ 
ment for the fungus. The Superior 
red clay is rather impervious to the 
passage of water and when once thor¬ 
oughly saturated retains surface water 
in hollows and in the soil structure more 
persistently than do lighter types of 
soil. This offers conditions favorable 
for the germination of the oospores of 
Aphanomyces which may be present 
and perhaps for the production of 
zoospores. On the other hand, the 
sandy soil referred to is underlaid with 
an impervious subsoil, which, in more 
level fields, holds standing water in the 
lower portion of the sand for several 
days after heavy rains, thus providing 
a similar environment for the develop¬ 
ment of the parasite. 
From this it appears that soil which is 
naturally retentive of water or in which 
water is held by reason of its relation 
to impervious layers furnishes the most 
favorable condition for the develop¬ 
ment of the disease. Such a supposi¬ 
tion is rendered very plausible by the 
character of the fungus and is sup¬ 
ported by other evidence, gathered not 
only in humid regions but in irrigated 
districts as well. The best examples 
of the relation of soil type and method 
of irrigation to the development of root 
rot have been found in the Gallatin and 
Paradise Valleys in Montana and near 
St. Anthony, Idaho. In the Gallatin 
Valley in 1921 this disease was found 
for the first time in a small field which 
appeared to have been overirrigated. 
The condition of the roots indicated 
that the infestation had developed after 
the plants were nearly grown, and 
although the root systems were thor¬ 
oughly rotted the yield from this field 
was not apparently reduced. Since 
this was the first observed instance of 
the development of the disease in this 
valley, and it offered an excellent op¬ 
portunity to obtain evidence which 
would indicate the severity which the 
disease might attain here, arrangement 
was made with the canning company 
for whom the peas were grown to have 
a portion of this field replanted with 
peas the following year. Such a field 
would not have produced an average 
crop of peas in a nonirrigated territory. 
Unfortunately the senior writer was 
unable to revisit this valley in the 
following year, but the canning com¬ 
pany reported a normal yield of peas 
with no conspicuous evidence of dis¬ 
ease. When the valley was revisited 
in 1923, a careful search of fields re¬ 
ported to have been used for this crop 
almost continuously for 10 or 12 years 
yielded but a single plant which was 
unmistakably diseased by this fungus. 
So far as this valley is concerned, there 
is no doubt that the fungus is present 
and that there are abundant facilities 
for its rapid distribution; yet, save 
possibly in cases of overirrigation, it 
appears that it is unable to become 
injurious. In contrast with conditions 
in this valley, fields in the Pine Creek 
district of the Paradise Valley about 
25 miles distant from the Gallatin 
Valley were found thoroughly infested 
and greatly injured by root rot both 
in 1921 and 1923. Peas have been 
grown extensively in both valleys for 
at least 12 years under very similar 
climatic conditions. Whether a dif¬ 
ference in soil structure or difference in 
the practice of irrigation has produced 
conditions favorable to the develop¬ 
ment of the disease in the Paradise 
Valley is not unmistakably apparent 
from observation. 
No soil survey has yet been made of 
the Paradise Valley whereby soil forma¬ 
tion there can be compared with that 
in the Gallatin Valley. There are, 
however, conspicuous differences in 
topography which suggest a difference 
in origin of the soils and a structure 
more retentive of water and conducive 
to seepage from higher levels in some 
fields of the Paradise Valley. 
If the water-holding capacity of soil 
or the retention of water in the soil is so 
necessary for the development of root 
rot, we may ask again whether the ap¬ 
parent immunity from disease which 
some Wisconsin fields have shown may 
not be due to soil conditions which pre¬ 
vent the development of the parasite. 
Before a final answer is given to this 
question a large number of fields which 
