s 
BULLETIN 70. 
laboratory as well as in the field; dryness and exposure to 
sunlight are especially liable to check its development. 
Test-tube cultures are very sensitive, hence results from in¬ 
oculations are apt to be misleading, since the culture mater¬ 
ial may be weak or dead when the inoculations are made, 
or the conditions under which the plants are growing may 
be unfavorable for the best development of the fungus. 
These experiments were conducted in the field with 
the exception of No. 2. *Check plants were used in the experi¬ 
ments and all of them remained in a healthy and vigorous 
condition. 
No. 1. On August 24 placed pure cultures of this fungus on twenty 
tuber stems and carefully covered the inoculations with grafting wax. 
In this experiment long young stems were selected in order to be able 
to make the inoculations some distance from the main stem. On Au¬ 
gust 29 eight of these stems were examined. All of them had brown- 
colored areas on inoculated surfaces. September 10 examined the re¬ 
maining twelve stems. Seven had deep scars under the wax and five of 
these seven developed new tubers above the wound. The remaining five 
inoculations gave no marked results. 
No. 2. July 7 inoculated twenty green stems on plants growing in 
pots in the greenhouse. Small incisions were made and particles of the 
culture material inserted. Check wounds were made in the same man¬ 
ner but not inoculated and all wounds were covered with grafting wax. 
August 21 three of the inoculated stems were found to be cut in two, 
eleven were deeply scarred and six remained uninjured. Plate XII. 
shows four stems taken from this lot. 
No. 3. Twenty inoculations made September 18 in the same man¬ 
ner as No. 1. Six of the inoculated tuber-stems were killed and the 
plants produced stemless tubers. Out of six root-inoculations four were 
killed and two remained healthy. Two of the eight inoculated branches 
were injured and six remained sound. 
No. 4. August 31, inoculated seven stems just below the sur¬ 
face of the ground. The operation was performed as in No. 1. These 
inoculations were examined September 12. Three produced a distinct black 
ring around the stems and four gave no marked results. 
No. 5. On the same day, August 31, fifteen tuber-stems and 
five roots were treated in the same way as in No. 1. These inoculations 
were made close to the main stem. September 12 five stems and the five 
roots were examined. All inoculations produced brown-colored areas 
on the inoculated surfaces. September 22 the remaining ten of these 
inoculations were carefully examined; seven of these had developed 
deep black wounds under the wax. The remaining three were completely 
cut off and small stemless tubers had developed on the main stem 
around the injured tuber stem. More or less of Rhizoctonia hyphae were 
found in all of the wounds. 
No. 6. On August 15th twelve green stems were slightly injured 
with a sterilized knife, and pure culture of the fungus was placed in the 
wounds and the inoculations were covered with wax. A careful exam¬ 
ination of these stems was made on September 6. Three of them were 
killed. (See Plate XI. Fig. 1.) Six developed marked wounds and three 
were healthy. Hyphae of the fungus were more or less plentiful in all 
of the wounds. The five check injuries healed and the stems remained 
vigorous. 
In any inoculation experiment it is necessary that uninoc¬ 
ulated plants be grown under the same conditions for the sake of 
comparison. In the following discussion such plants are designated as 
checks. 
