38 
Journal of Agricultural Research 
Vol. XIV, No. I 
It is evident from the preceding data relative to aphids which have 
fed on blighted plants that a small percentage of their offspring, although 
these may have have been bom and reared on plants other than spinach, 
may produce infections of blight when they are transferred to healthy 
spinach plants. Inoculations made with the juices of lettuce, eggplant, 
and supposedly healthy spinach produced no infections; hence, it is 
unlikely that either the lettuce or the eggplant served as alternate hosts 
for the inciting factor of the disease. The possibility that the blighted 
condition was due to a mechanical or other stimulus produced directly 
by the insect was disproved by the fact that aphids from the regions 
mentioned, where as yet the occurrence of spinach-blight has not been 
reported, were incapable of producing infections on healthy spinach 
unless they had fed on a diseased plant previous to their transference to 
a healthy plant. It was also found that the juice of Norfolk aphids, 
although bom and reared on plants other than spinach, occasionally 
produced infections of blight when inoculated into healthy plants. The 
percentage of infection obtained by transferring the local strain of aphids 
from lettuce, eggplant, or peppers to healthy spinach plants was small. 
The transfers of local aphids from supposedly healthy spinach to known 
healthy spinach resulted in a larger number of infections than*in cases 
where the aphids were transferred from lettuce or eggplant to healthy 
spinach. As it subsequently appeared, these supposedly healthy plants 
were diseased at the time the transfers were made from them to the 
known healthy plants. They became infected in all probability through 
the agency of the original aphids transferred from the lettuce seedlings. 
The plants were small and the aphids were numerous; therefore it was 
difficult to distinguish between the early visible symptoms of the disease 
and the somewhat yellowish condition caused by the attacks of numer¬ 
ous aphids. Subsequent inoculations proved that the juice taken from 
these plants was virulent; hence, it was a simple matter for infections 
to be carried from these to other plants when the transfers of insects 
were made. Inoculations made with the juices of lettuce, eggplant, and 
peppers used as food for the aphids before their transference to healthy 
spinach gave no indications of any infections. 
In the light of these findings—namely, (i) that the offspring of local 
virus-bearing aphids, although bom and reared on plants other than 
spinach, are capable under certain conditions of producing infections of 
blight in healthy spinach plants to which they have been transferred; 
(2) that the juices of the plants other than spinach upon which these 
aphids were reared were nonvirulent; (3) that aphids of foreign strains 
are incapable of producing the blight on healthy spinach, unless they have 
first fed on diseased plants—the assumption* must be taken that, whatever 
the entity is which caused the pathological transformations in the growth 
and development of normal spinach plants, it must be in some manner 
transmitted from the parent aphids to their offspring, as the offspring in 
turn may cause infections in healthy plants upon which they feed. 
