20 
variety, it tends to be yellow-green or more reddish. With some' 
varieties there occurs also an almost violet color, as for example, in 
the German sort, Hetmann. The intensity of the color varies hi dif- 
ferent years, and it appears that dry seasons bring a more intense' 
color than moist seasons. 
The time of onset is early, as compared with Fusarium wilt. The 
first case observed by the writer in Germany was in Giessen about 
June 20. Reference to the German records will show that the date 
when leaf -roll is first observed varies in different years. In 1907, for 
instance, many varieties were strongly attacked as early as June 24, 
while in 1909 the corresponding date in July saw less leaf -roll in their 
experimental plants. The date when leaf-roll appears in this country 
is not well fixed. Growers in the Greeley, Colo., district, where late 
planting is the rule, report having noticed the rolling of the leaves 
late in July. Leaf -roll did not develop last year (1913) in the 
Mitchell (Nebr.) district until about August 15, whereas the preceding 
outbreaks had come much earlier. 
The effect on the plant is to check development. There is a lessening 
or cessation of growth. The shoots remain short and the leaves 
stand more upright. 
In this respect varieties differ. The following show the staring growth very clearly: 
Magnum Bonum, Hetmann, Richter's Imperator, etc., while Daber shows it but little. 
On such stalks the leaves, flowers, and berries are frequently smaller. For example, 
the berries of Hetmann on badly diseased plants in 1908 were only the size of peas, 
while those from healthy stalks were the size of cherries. Badly diseased plants have 
often no tubers or only a few. Such plants are either very weak and die early or the 
foliage may be comparatively well developed and remain living to the end of the 
vegetation period. (Appel and Schlumberger, 1911.) 
The different degrees of leaf-roll are also shown in the illustrations. 
Plate V shows large plants with the upper leaves strongly rolled, 
while the plant in PI. IV, fig. 2, is small and weak and represents 
the last stage of leaf-roll, having doubtless come from a tuber pro- 
duced by a diseased plant. There is, however, no such shortening 
of stems and leaf ribs as occurs in curly-dwarf, with its resultant 
deformation of the plant. 
The duration of life of the plant in most cases appears to be 
shortened by leaf-roll. This is a relative matter, since (in com- 
parison with healthy plants) the leaf-roll cases may die earlier, as 
would be expected of sick plants, or they may stand until killed 
by frost, while (in comparison with the rapid death of American 
potatoes attacked by Fusarium wilt) the endurance of leaf-roll is 
one of the striking differences between these diseases. 
The endurance of the seed piece as a character of leaf-roll is an 
interesting point frequently mentioned in the German literature. 
When Schultz [Soest] (1905) called attention to the first outbreak of 
leaf-roll, he laid special emphasis on the fact that the seed tubers 
