258 
Journal of Agricultural Research 
Vol. XXI, No. 4 
on that side may show internal browning, or again the entire plant may 
droop. The wilting may come about very suddenly or slowly. The 
first manifestation of wilt often appears after a period of wet weather of 
several days' duration, such weather apparently favoring infection. 
More of the wilt is seen in hot, dry weather. Often a plant may recover 
temporarily during moist weather or during a cool night after a hot, dry 
day, which has resulted in the appearance of wilt. Sometimes this 
recovery leaves a shriveled tip or margin on some of the leaves. The 
ultimate result of the wilt, in the more severe cases at least, is the com¬ 
plete death of the plant. After wilting the leaves dry and turn black, 
later dropping from the plant and leaving the bare black stalk and 
branches. 
In many plants infection was present late in the season but was not 
severe enough to cause permanent wilting or death of the plant. In 
such cases marked dwarfing occurred. In a field at Dothan, Ala., it 
was easily possible to pick out infected plants that showed no external 
signs other than dwarfing. Plate 55, A, reproduced from a photograph 
taken at Dothan, Ala., on August 24, 1918, shows from left to right, a 
dwarfed and a wilted plant (both of which showed unmistakable in¬ 
ternal signs of the bacterial wilt) and a large normal plant. 
A disease due to a root trouble and entirely distinct from the wilt, 
but showing some signs similar to it, was found in the vicinity of Miami, 
Fla., and at other points especially in muck lands. These plants ap¬ 
peared to be affected by asphyxiation of the roots due to too high a 
water table. Many such plants were observed with the root systems 
entirely dead and often with the tap roots rotted off 3 or 4 inches below 
the surface of the ground. Such root conditions resulted in the death 
of the top of the plant, manifested by wilting and drooping of the leaves 
and twigs and finally by the death and blackening of the entire plant 
(PI. 56). 
The bacterial wilt can be distinguished easily from the disease de¬ 
scribed above and from any other known disease of the castor bean by 
the typical browning of the vascular system near the base of the plant. 
In the severer cases this browning is seen in the entire vascular ring, 
penetrating more or less deeply into the woody part of the stem. In 
cases of light infection, such as in the dwarfed plants mentioned here¬ 
tofore, the browning may be seen in only a few bundles, all possibly on 
one side of the stem. In fact, cases were observed in which only a 
single bundle gave this manifestation of the presence of disease. In 
addition to the browning it is always possible with the aid of a good 
hand lens to observe drops of bacterial exudate at the freshly cut ends 
of the vascular tubes, particularly if the plant is still green. Sometimes 
it is necessary to pinch the end of the stem to force these drops to the 
surface. 
