Aug. ii, 1923 
Irish Potato Foliage Degeneration Diseases 
261 
in plots or fields where both mosaic and leafroll are common that vines 
receive infection during the season which does not develop into external 
symptoms until the following season. For example, plants with appar¬ 
ently normal and healthy foliage throughout the season nevertheless 
produce tubers which in the following season develop plants with various 
stages of mosaic or leafroll. Evidently the sprouts of such tubers would 
have significance with reference to the foliage condition of the plants 
which they produced rather than of the plants from which they came. 
Further, in the case of net-necrosis of the tuber it has been shown by 
Schultz and Folsom ( 12 , p. 65-ji) that this condition suddenly appears 
and often as suddenly disappears so far as the symptoms are concerned, 
and that in its correlation with leafroll it depends upon “recency of infec¬ 
tion.” Consequently, with reference to this trouble also, the symptoms 
of the plants resulting from net-necrosis tubers are of more significance 
than those of the plants producing them. 
Blodgett, Femow, and Perry report in an abstract on “Testing Seed 
Potatoes for Mosaic and Leafroll” (5) that “tubers indexed as leafroll 
grew sprouts generally thinner than healthy potatoes but not always 
of the extreme spindling-sprout type,” and state that by a preliminary 
sprouting method all but 3 per cent was removed from two lots contain- 
ing 50 per cent of leafroll. These writers also secured partially successful 
results in eliminating mosaic and leafroll from seed stock by growing one 
seed piece from each tuber as an early crop in the field previous to planting 
the main crop. 
In the spring of 1921 about 60 hills were planted in the experimental 
plot with seed pieces from tubers which had sprouted in storage and 
whose sprouts showed a more or less spindling condition. Of these, 20 
hills were of the Burbank variety and 40 hills were Green Mountain. 
The 20 hills of Burbank (No. 91, 1921) planted with seed pieces from 
tubers all of which had developed spindling sprouts showed 100 per cent 
characteristic leafroll. A control row of 26 hills (No. 92, 1921) of the 
same variety and lot but planted with tubers which had apparently 
normal sprouts, produced 92 per cent healthy hills and 8 per cent leafroll 
hills. Three of the leafroll hills from No. 91 (1921) and one healthy hill 
from No. 92, (1921) are shown in Plate 3. 
The 40 hills of Green Mountains were planted in single tuber units 
with tubers selected from various samples of the preceding season, these 
tubers having developed in storage sprouts of more or less marked spindli¬ 
ness. Without exception, each hill of every tuber unit developed leafroll 
in varying degrees of seriousness. All the tuber units were planted in 
the same order, the seed pieces from the bud end or apex first and the 
others progressively in order to the stem end. With a large degree of 
uniformity the plants from the bud-end pieces were larger, more vigor¬ 
ous, and more productive, while a rather uniform decrease in size and 
productivity characterized the plants from the middle and stem-end 
pieces. Plate 4, A, B, C, and D, shows four of the five plants of tuber 
unit series 75 (16-1) illustrating characteristic leafroll symptoms and 
gradual decrease in size. The photographs of these hills were taken 
with the camera at the same distance in each case. All of the plants 
were rather small, the smallest being about 8 inches in height. In Plate 
5, A, 75, may be seen the sprouted tuber from which these plants were 
grown. It will be observed that there is one rather vigorous sprout at 
the apex and that the remaining sprouts are more or less spindling, a 
condition very common in connection with this type of degeneracy. In 
