POTATO WILT, LEAF-BOLL, AND BELATED DISEASES. 5 
with the leaf-roll group, but the writer has not seen this disease and 
has been unable to arrive at a satisfactory conclusion concerning its 
relationship to any known American trouble. The causal organism 
has not yet been properly described. 
A second bacterial disease of German potatoes is referred to by 
Spieckermann (1911) as different from Appel's ring disease. This 
the writer saw at Muenster and found to be unlike any of the weD-* 
known American diseases. 
FUSARXUM WILT. 
DESCRIPTION OF DISEASED PLANTS. 
The distinctive characteristics of this disease are a rolling or wilting 
of the leaves, premature death of the foliage, and the occurrence of 
the fungus Fusarium oxysporum (Schlecht) Sm. and Sw. in the lower 
part of the stem, in the stolons, and frequently in the tubers also. 
In detail, the appearance of potatoes attacked by Fusarium wilt 
varies according to the severity of the infection, the age of the plants,, 
and the variety. 
The time of onset varies with the degree of infection. Where 
diseased seed stock has been used, there is often defective germina- 
tion and an irregular stand of plants of uneven size. As a rule, 
however, the disease is not noticeable till the plants are a foot or 
more high, and in most cases it does not become generally prevalent 
till midsummer, while it is characteristic of moderate infections that 
the plants die only two or three weeks in advance of their normal 
time of maturity. 
Wilting of the foliage is to be observed in the more rapid types of 
the disease, but is less marked than in some other Fusarium wilts, 
such as that of watermelon, for instance. 
The name "wilt" has been retained because it is in common use 
for this and related maladies, though the name "Fusarium blight of 
potatoes" has also been applied. The foliage symptoms may be 
described by either term. They are those of a plant whose water 
supply has been gradually shut off by fungus invasion of the lower 
stem. 
The lower leaves droop and die first, the upper ones wither or wilt, 
and the entire plant dies prematurely. (PI. I.) The leaf -roll that 
accompanies wilt differs from the true leaf-roll in that the former 
lacks turgidity and the leaves die within, a few days. 
The color of plants in the first stages of wilt may be a lighter green 
than is normal. This frequently turns to yellow, especially if the 
progress of the disease is slow, when the entire plant becomes yellow 
and the field takes on a very spotted appearance. It is different 
with the true leaf-roll, where the yellowing is, in the American types, 
more confined to the upper leaves and is accompanied on many 
