July i, 1918 
True Nature of Spinach-Blight 
19 
DIRECT TRANSFERS OF MACROSIPHUM SOLANIFOLII FROM DISEASED TO HEALTHY PLANTS 
On each of 12 vigorous plants growing in field cages were placed 10 
adults of Macrosiphum solanifolii from diseased plants. Eleven of the 
twelve plants developed positive symptoms of the disease. The incuba¬ 
tion period varied from 12 to 30 days, the average being 17.8 days. One 
plant remained healthy until March 2, when the last record was made. 
DIRECT TRANSFERS OF RHOPALOSIPHUM PERSICAE FROM DISEASED TO HEALTHY PLANTS 
Another series consisted of 12 plants inoculated in a similar man¬ 
ner, except that 10 adults of Rhopalosiphum persicae were placed on each 
of 12 healthy plants. The aphids were collected on the same diseased 
plants from which a number of Macrosiphum solanifolii were taken for 
use in the first series. Again eleven plants developed symptoms of the 
disease between 12 and 30 days after they had been inoculated. The 
average incubation period was 17 days, or 0.8 day less than for the 
M. solanifolii series. 
INOCULATIONS WITH THE JUICE OF CRUSHED APHIDS COLLECTED FROM DISEASED SPINACH 
Twelve healthy plants were inoculated with the juice of crushed 
Macrosiphum solanifolii collected on diseased plants. The inoculations 
were made by means of needle pricks. Six plants became infected in an 
average period of 21.1 days. Likewise 12 plants were inoculated with the 
juice of crushed Rhopalosiphum persicae from diseased plants. These 
innoculations resulted in three infections in an average time of 24.6 days. 
INOCULATIONS WITH VIRUS FROM PLANTS UPON WHICH THE APHIDS FED 
Another series f 12 plants were inoculated with the virus taken from 
the crushed leaves of diseased plants upon which the aphids were feed¬ 
ing before they were transferred to healthy plants. The virus was 
pricked into the leaves by means of a sterile needle. Nine plants devel¬ 
oped symptoms of blight in an average time of 20.6 days. As a check on 
this series 12 plants were pricked with a sterile needle. No cases of in¬ 
fection resulted, and the plants remained healthy until the experiment 
was closed. 
TRANSFERS OF APHIDS BORN AND REARED ON LETTUCE TO HEALTHY SPINACH 
As a control on the previous transfers made with insects from diseased 
spinach, 10 healthy plants were selected, and on them were placed a 
number of adults of Macrosiphum solanifolii born and reared on lettuce, 
and which had not fed on spinach until transferred to the plants in this 
series. The parents of these aphids were collected in the field from sup¬ 
posedly healthy spinach. Two of the 10 plants developed positive 
symptoms of blight, the first appearing on the twenty-first and the sec¬ 
ond on the thirtieth day after the transfers had been made. The eight 
