130 Dale — On the Cause of ‘ Blindness ’ in Potato Ttibers. 
tubers themselves, through the heel. The track of the fungus may easily 
be traced with the naked eye by means of the brown coloration. On some 
of the new tubers were many long, straight, brown hyphae, especially near 
the eyes. These hyphae apparently attack the tubers by means of the eyes 
and spread through the superficial tissues of the tubers. Possibly the 
hyphae may also obtain an entrance through the lenticels. 
Microscopic sections show that the mycelium on the underground 
shoots is partly external and partly in the cortical tissues, but that it never 
penetrates as far as the vascular tissues. Some of the external hyphae are 
long, straight, and relatively thick-walled, of a light brown colour, and 
branching at long intervals almost at right angles to the main hyphae. If 
kept in damp air these hyphae produce the slender colourless mycelium of 
Verticillium albo-atrum. The old mycelium forms, both on the living plant 
and also on cultures of sterilized potato tuber, a dark brown resting mycelium 
with small rounded segments containing numerous drops of oil. This 
mycelium, when kept damp, also puts out colourless hyphae. 
According to Reinke and Berthold 1 the disease known as leaf-curl is 
also due to Verticillium albo-atrum . These observers found a mycelium in 
the vascular tissues of the subaerial stems, and also in the cortical tissues 
of the subterraneaii stems. In both cases the mycelium was that of Verti- 
cillium albo-atrum. The fungus was not found in the tubers except near 
the heel. Reinke and Berthold distinguish three types of fungus affecting 
two generations of potato plants, and state that some races of potato are 
more liable to infection than others. 
The late Professor Marshall Ward 2 found what seems to be the sub- 
aerial mycelium mentioned above, and also noticed some of the other 
symptoms described by Reinke and Berthold, but apparently not leaf-curl. 
He succeeded in tracing the fungus down the stem into the heel of the new 
tuber. 
None of these observers seem to have noticed the fungus in tubers 
stored through the winter, nor to have observed the destruction of the 
‘ eyes \ 
Both the disease known as ‘ blindness ’ and that causing ‘ leaf-curl ’ 
seem to be due to Verticillmm albo-atrum , 3 and tubers from crops 
affected with these diseases should not be used for ‘ seed ’, though they are 
quite fit for culinary purposes and generally keep well on account of the 
corky layer round the cortex. 
1 Reinke and Berthold : 1. c. 
2 Marshall Ward : A Potato Disease. British Association Report, Bristol, 1898. 
3 Aote. Leaf-curl and leaf-roll almost certainly occur as symptoms in other diseases. 
