50 
Journal of Agricultural Research 
Vol. XXI, No. i 
produce only culls, and these will result in practically a total loss to the 
grower. The results of studies dealing with the effect upon yield are 
given in Table I. 
Table I .—Effect of leaf roll upon yield 
Lot No. 
Variety. 
Total 
number 
of hills. 
Percent¬ 
age of 
hills leaf- 
roll. 
Total 
yield (in 
pounds). 
Yield 
rate (in 
pounds 
per hill). 
1919-AF 17, 18, 19. . . 
Irish Cobbler.r.. . 
14 
0 
20 
I- 43 
T9T9— AF 2 0 and 3 t . 
.do. 
6 
IOO 
5 
•83 
1920-20. 
Irish Cobbler, strain A. .. . 
1.19s 
O 
2,052 
I. 72 
1920-24 . 
909 
IO 
1, 220 
i- 34 
1920-22 . 
Irish Cobbler, strain B. ... 
639 
O 
943 
1. 47 
1920-23 . 
616 
3-3 
722 
1. 17 
1920-28. 
150 
100 
37 
*25 
T^o-26 and 29 . 
Irish Cobbler . 
276 
IOO 
ici 
. 41 
1920-P. I. 13 . 
" 8 
IOO 
DO 
4-5 
.56 
1920-P. I. 15 . 
12 
0 
21 
i- 75 
i The year of planting is given as part of the lot number. 
In Table I the two 1919 lots and lots 1920-P. I. 13 and 15 were 
hill-selected and planted according to the hill- and tuber-unit method. 
The others were planted in bulk. As indicated, in two cases a single 
strain was divided into two or three lots, which may be compared with 
greater value than lots from different strains. The difference in yield 
between the two comparable 100 per cent leafroll lots—those planted in 
bulk in . 1920—is due largely to differences between the strains. It is 
doubtful whether the small amounts of leafroll in lots 1920-24 and 
1920-23 are entirely responsible for the reduction in yield rate as com¬ 
pared with the corresponding healthy lots, 1920-20 and 1920-22. 
However, it is clear that the yield rate of entirely leafroll stock is very 
materially reduced as compared with that of healthy lots. 
When net-necrosis appears as a symptom of leafroll, tubers which 
otherwise could be used for culinary or exhibition purposes become of 
less value. Even the usual severe effects of leafroll upon the plant are 
accentuated by the phloem-necrosis of the tuber, as shown in Plates 5, B, 
and 6, A. The comparative infrequency of its appearance makes it less 
important than leafroll, but its relation to leafroll makes the latter, 
as the fundamental trouble, still more undesirable. 
Plate 7, A, B, shows a row, and Plate 7, C, shows a plot of dwarfed 
plants produced by net-necrosis seed. The effect of net-necrosis upon 
the yield is considered in Table II. Data concerning the lots grown at 
Highmoor Farm (of the Maine Agricultural Experiment Station, in south¬ 
ern Maine) and in 1917 at Aroostook Farm (Station Farm in northeastern 
Maine) were secured, respectively, by Dr. W. J. Morse, plant pathologist, 
and Mr. G. B. Ramsey, then assistant plant pathologist. These data, 
in so far as they are concerned with symptoms, are indicated in the 
table by quotation marks. 
