POTATO FAILURES. 
7 
which is known in some sections as “Collar Rot” or “Black 
Ring” of the potato plant. Badly affected plants wilt sud¬ 
denly and are soon dead and dry. Frequently, however, 
the attacks on the stem are not so severe but the wounds 
are so situated as to prevent the free transportation of plant 
food to the tuber stems, thus cutting off the food supply to 
the growing potatoes, which consequently remain small. If 
the injuries prevent the assimilated food from being stored 
in the subterranean parts of the plant, large tops are pro¬ 
duced, and green tubers often form in the axils of the 
leaves, thus giving rise to the so-called “Aerial Potatoes”. 
(See Plate VIII.) When the root system of such plants is 
more or less injured, the leaves usually take on a lighter 
color and have a tendency to fold. The stems become 
thicker, and grow prostrate, giving the plants a bushy ap¬ 
pearance. 
A similar condition is brought about by the attacks of 
the fungus on the tuber-stems. Young tubers are frequently 
cut off by the fungus as shownin Plate XI. Fig 2. The yield is 
often materially reduced in this way and it is not uncom¬ 
mon for all of the tubers to be cut off as shown in Plate VI. 
When the tuber stems are less severely injured, but the 
wounds are severe enough to interfere with the flow of plant 
food to the young potatoes, the buds on these stems just 
above the wound often develop tubers. But the fungus 
may continue its work and again injure or cut off the stem 
above the newly formed tubers. When the main stem is 
infected with the disease, the tuber-stems are apt to be cut 
off before they have made much growth. In such cases 
blind or adventitious buds may push out and form on the 
main stem around the injured member and develop short¬ 
stemmed or stemless tubers as shown in Plate IX. where a 
typical cluster of “Little Potatoes” have formed. If the 
root system is also invaded by the disease, the vitality of 
the plant is reduced and it puts out few or no subterranean 
stems. The tuber-stems which do grow are probably weak 
and soon cut off by the fungus. Such plants set few or no 
tubers and usually take on the peculiar top development de¬ 
scribed above. 
INOCULATION EXPERIMENTS. 
The following series of inoculation experiments was un¬ 
dertaken with cultures of Rhizoctonia to prove that the dis¬ 
ease is parasitic and that its attack on the potato plant may 
produce the conditions described above. Pure cultures were 
readily obtained from the sclerotia on tubers. Conditions 
have a marked influence in the growth of this fungus in the 
