16 
Bulletin 69. 
Inoculation experiments were undertaken with potato Rhizoc- 
tonia, both with pure cultures and with the sclerotia as they occur on 
potato tubers. Peas were germinated in the laboratory and when 
the caulicle was about an inch long the inoculation was made. 
Some of the fungus from the cultures was placed between the 
caulicle and the cotyledons; then the peas were planted in coarse 
river sand in the greenhouse. Peas that were not inoculated were 
planted at the same time to serve as a check on the work. The re¬ 
sult of the experiment shows that the fungus occuring on the potato 
is parasitic on the pea, as the roots of all inoculated plants were 
badly diseased and in some instances the caulicle of the young plant 
was cut off. But in no instance were the plants killed, as they 
threw out new roots above the injury and were able in a measure to 
overcome the disease. Roots of the pea plants that were injured by 
the fungus in these inoculation experiments are shown in Plate VI., 
Fig. 1. The check plants grown under the same conditions, but 
not inoculated, showed no signs of disease. These experiments were 
repeated and varied by placing portions of the fungus under both 
caulicle and plumule. Rhizodonia sclerotia taken from potatoes and 
started into vigorous growth by placing them in a moist chamber 
over night were used in the same way; the results were the same as 
before. 
These experiments do not prove conclusively that the so-called 
Rhizodonia disease of potatoes is the cause of this trouble with peas, 
but the indications point strongly to this conclusion. It is known 
that this fungus is destructive to a great variety of plants and these 
experiments show that it may injure peas. That it did not kill the 
pea plants in the inoculation experiments may be due to the fact 
that conditions in the greenhouse were not suitable for the best 
development of the fungus. The failure of the fungus to kill the 
peas that were grown in the greenhouse in soil from an infested field 
must also have been due to unfavorable conditions. 
As a result of these observations and experiments it is safe to 
conclude that the pea disease is due to a fungus that is in the soil 
when the peas are planted. There is no practical way of detecting 
its presence until its effects are seen on the pea plants, consequently 
the discovery of a method of treatment would seem to be a difficult 
matter; some suggestions, however, obtained from the study of other 
plant diseases may be of value. 
First—The heavier soils should be avoided for pea growing, as 
root diseases, especially the fungus that attacks potatoes as mentioned 
above, is much more severe on such soils. 
Second—By deep plowing the diseased surface soil may be 
buried so deeply that the fungus will not come in contact with the 
young roots. After the pea plants are thoroughly established it is 
probable that the fungus will have only a slightly injurious effect, 
