Apr. i, i93i 
Leafroll , Net-Necrosis, and Spindling-Sprout 
7i 
In the 1920 generation of the three sublots that showed net-necrosis 
in 1919—that is, the first, third, and fourth as given in Table XI—the 
inclusion of progressively larger sets of tubers tends to reduce the per¬ 
centage of net-necrosis. Thus, inherited net-necrosis is less common as 
the average tuber weight is greater. In the 1920 generation of the other 
three sublots a progressive increase in tuber weight is accompanied by a 
rather marked increase in the percentage of both leafroll and net-necrosis 
until 5 or 6 ounces are reached, except in sublot 1 of lot 126, where the 
increase of tuber weight has more effect on net-necrosis percentage than 
on leafroll percentage. Here, in the sublots with initial net-necrosis, 
the fundamental relation is one between leafroll infection and tuber 
weight, with its exact cause unknown. Initial net-necrosis shows a 
similar relation to tuber weight because it is proportional to leafroll 
infection. 
It has been pointed out that inheritability of net-necrosis tends to be 
varietal. Inherited net-necrosis may tend to be more common as the 
tubers are lighter in weight. Recency of leafroll infection may deter¬ 
mine the development of net-necrosis within a given variety. Finally, 
net-necrosis resulting from recent leafroll infection may tend in a given 
strain to be more common as the proximity to leafroll hills is greater 
and to be less- common in the lighter-weight tubers, both usually in 
correlation with a similar tendency shown by the leafroll infection itself. 
It may also be pointed out that there was a great difference in leafroll 
infection, as shown in Table VIII, between the first sublot of lot 126 and 
that of lot 110. This was not necessarily due to the facts that in lot 126 
the healthy hills were of the same variety (Green Mountain) as the 
diseased hills alternating with them and that in lot no they were of the 
Green Mountain variety, while the diseased ones were not. The latter 
lot, showing much less leafroll (and net-necrosis) in 1920, was in a field 
in 1919 in which aphids were later in appearance and fewer in numbers 
than they were in the plot in which the former lot was grown. Also, it 
was over 150 meters from the weedy border of the field, while the former 
lot was about 25 meters from one end of an acre plot with a permanent 
weed patch at both ends and along one side and so was much nearer to 
the probable sources of newly hatched aphids. The most important 
difference seems to have been that of abundance of aphids, which have 
been shown to be capable of transmitting leafroll. 
TEMPERATURE 
Jones and others ( 12 ) have demonstrated that a type of net-necrosis 
may be induced by certain conditions of low temperature, but have dis¬ 
tinguished ( 12 , p . 22) between frost-necrosis of the net type and inheri¬ 
table net-necrosis. The same distinction is made by Coons (7, p. 37). 
One of the writers at Orono followed the methods of Jones and his co¬ 
workers (12), except that outdoor conditions were used, and induced 
