son that it is difficult to find a sack of potatoes free from all traces 
of the disease. It lives over winter in the cracks of rough and rus- 
seted potatoes and in the ulcers of scab, and also in what appears to 
be patches of dirt which stick closely to the surface of the potato. 
By looking closely at these dirt-like appearing objects, which are 
well shown in Fig. 2 , Plate I., it will be seen that they are not com¬ 
posed of ordinary soil. In fact, they are made up of the closely in¬ 
terwoven root-like organs of the fungus. 
This tiny plant also produces an abundance of seed-like bodies 
or spores which help to spread it. They are borne only on green 
potato vines and just above the surface of the ground. Here a thin, 
delicate layer is formed that looks like a slight deposit of alkali, and 
the spores are borne on the tips of the threads of which it is com¬ 
posed. 
A Poor Stand of Potatoes. When diseased potatoes are used 
for see^l, or when clean potatoes are planted in infected soil, the 
fungus starts into growth with the young potato plant. The tender 
shoots are often attacked, with the result shown in Plate II. On the 
right are two shoots, which were rotted off by the fungus before 
they reached the surface of the ground. This illustrates how a poor 
stand of potatoes is often brought about. The other two were badly 
injured and might have become mature plants, but affected with the 
familiar collar rot or black ring. 
Vines and no Tubers. The most damage is done, however, by 
cutting off the tuber stems, and this portion of the potato plant is 
especially liable to attack. These stems are often cut off as fast as 
they grow out, thus leaving no place on which tubers may form. 
But in some instances a cluster of small or “Little Potatoes’' form 
around the main stem, seemingly the result of girdling by the 
fungus. 
Potato Scab. The potato tubers are often made rough and 
scabby by the growth of the disease on their surfaces. (Plate I., 
Fig. 3 .) All gradations of these injuries may be found, from a 
rough or russeted appearance to deep scabs or ulcers that greatly 
injure the appearance of the potato. Singularly enough, scab is 
more common in the best potato soil than it is in localities where 
the crop is precarious. Sandy or gravelly soils, when first brought 
under cultivation, often give a large per cent, of scabby potatoes, 
but after one or more crops of alfalfa have been plowed under, this 
tendency is partially corrected. 
Potato Blight. Potato blight, or the dying of the leaves and 
vines before the crop is mature, is commonly thought to be entirely 
due to diseases which attack the top of the potato plant. We have 
not found it so in Colorado. Spraying experiments with Bordeaux 
5 
