52 
Journal of Agricultural Research 
Vol. XXI, No. i 
The comparisons in Table II deal with small lots for the most part, 
chiefly because of the scarcity of net-necrosis material. They indicate 
that while leaf roll without net-necrosis reduces the yield greatly, both 
together reduce it still more. 
TRANSMISSION OF LEAFROEL 
TRANSMISSION BY TUBERS 
Transmission of leafroll through the tubers has been noted by different 
investigators studying this malady (15, 17, 22). Observations made by 
the writers upon the same strains of leafroll diseased stock since 1916 
show that these stocks consistently have developed plants with the 
characteristic leafroll symptoms. Tuber production has practically 
ceased in some of these. Others continue to form plants and tubers 
as in 1916 but always show leafroll. 
TRANSMISSION BY GRAFTING 
TUBERS 
Since mosaic of Irish potatoes was successfully transmitted by the 
writers by means of tuber grafts (20 ), similar methods were followed 
with leafroll. In May, 1919, 20 tubers of approximately the same size 
and shape were selected from healthy and from leafroll stock. The 
freshly cut surfaces of a healthy half tuber and a leafroll half tuber 
were brought into intimate contact and were kept there with rubber 
bands. Planting followed immediately. The other half of each of the 
healthy tubers was planted separately as a control. A set of 7 tubers 
grafted with the halves from healthy tubers served as an additional 
control. 
At the end of the growing season all the control plants were free from 
leafroll. Three of the 20 healthy half tubers grafted on leafroll half 
tubers had produced plants with leafroll. Upon examination it was 
found that these 3 were the only ones which had formed organic union 
with the corresponding diseased halves. One of the 3 plants thus inocu¬ 
lated through tuber grafting, together with the control, is shown in 
Plate 8. These results confirm similar ones secured by Quanjer (17). 
STALKS 
In the summer of 1919 a healthy stalk in each of three hills of the 
Green Mountain variety was grafted with a scion taken from a leafroll 
plant of the same variety. The stalks at the time of graf ting were about 
16 cm. tall. At the same time and in a similar manner a stalk in each of 
four Irish Cobbler hills was grafted. These grafts were in the open field, 
in three 4-hill tuber units. 
By the end of the growing season in the seven different grafted hills 
each of the shoots growing from the stock just below the graft developed 
