262 
Journal of Agricultural Research 
Vol. XXV, No. 6 
general, spindliness tends to begin in the sprouts at or near the stem end 
of the tuber, one or more sprouts at the apex often remaining normal in 
size and appearance except in the most extreme cases, such as is shown in 
Plate 5, D, 85, where all the sprouts have become spindling. That the 
varying degrees of spindliness of sprout are correlated with differences in 
vigor and productivity of the resulting plants is illustrated in Plate 4, A, 
B, C, D; Plate 6, A, B, C, D, B; and Tables I and II. 
Table II.— Yields in grams from average hills of Burbank plants which exhibited extreme 
and mild leafroll symptoms and normal foliage , respectively 
Record 
No. <1921). 
Condition of 
sprout. 
Yields from average hills— 
Total. 
t 
Average 
per hill. 
Condition of 
plants. 
1 
3 
3 
4 
91a. 
91b. 
9 a. 
Spindling. 
Normal. 
120.4 
329-9 
835-7 
63. 2 
195-9 
584 
0 
O 
591 
0 
0 
613 
183.6 
525- 8 
2, 624. s 
91. 8 
262.9 
656.1 
Extreme leafroll. 
Mild leafroll. 
Healthy. 
In Table II, No. 91a and 91b included tubers selected for very much 
marked spindliness of sprout. As indicated previously, all the plants 
from these tubers developed characteristic leafroll. The leafroll symp¬ 
toms, however, varied in seriousness and the plants showing extreme 
symptoms, being much dwarfed, were indicated as 91a, while those of 
larger growth but still with well-marked leafroll characters, were 
designated as 91b. Average hills from each of these groups were selected 
and the yields weighed, with the results given in the table. For com¬ 
parison, four average healthy hills from lot 92 (1921) were selected 
and the yields weighed. The results correspond closely to expectation 
as governed by the condition of the foliage. Wide variation in yields 
between the two types of leafroll appears, and a difference nearly as 
great between mild leafroll and healthy hills. 
CORRELATION OF NET-NECROSIS WITH SPINDLING-SPROUT AND LEAFROLL 
In cutting the tubers of lot 91 (1921), referred to in preceding para¬ 
graphs, it was noted that every tuber showed typical net-necrosis of 
the sort illustrated in Plate 6, A, affecting a portion of its tissues. These 
tubers had been selected for investigation because of the extreme 
spindliness of the sprouts which had developed in the storage cellar 
during early spring. In the experimental plot Hie plants from these 
tubers developed 100 per cent leafroll. Many of the hills were very 
weak and some seed pieces produced no plants at all. In lot 92 (1921) 
of the same variety selected for normal sprouts no net-necrosis was 
found, and of this lot, as noted previously, 92 per cent of the plants 
were healthy and 8 per cent showed leafroll. A tuber unit series from 
a net-necrosis tuber is illustrated in Plate 6. Three of the four seed 
pieces of this tuber showed necrosis of the cortical region and from 
near the edges of the necrotic tissue in two of the pieces sprouts which 
were thin and spindling had developed. The seed piece from the 
apex of the tuber developed two sprouts apparently normal, but the 
plant from this piece, as well as those from the pieces showing necrosis, 
developed both leafroll and mosaic symptoms. The occurrence of the 
mosaic symptoms in this instance, as in some others observed, is be- 
