July i, 1918 
True Nature of Spinach-Blight 
25 
series showed mottled leaves; but the controls remained healthy. These 
pots were kept under observation for the next month, and during this 
time the majority of the seedlings in all of the seed lots became mottled 
and stunted in growth, thus indicating that it made little difference as to 
the source of seed of the Savoy strain of spinach grown from commercial 
seed as regards the resistance to blight. 
Farm D.—Blighted plants were collected from two fields on farm D 
and aphids from some of these plants were placed on a large pot con¬ 
taining about 100 spinach plants 13 days old. A similar pot of seedlings 
served as a control. % Eighteen days after inoculation some of these 
seedling plants had developed the mottled leaves typical of blight. 
Twenty-nine days later some of the blighted plants were alive, but in 
advanced stages of the disease. Control plants remained healthy. 
These results indicate that diseased plants scattered over fields are 
caused by the same virus which produces large areas of blighted plants. 
Farm B.—Blighted plants were collected from farm B and brought to 
the Station, where a number of RhopcUosiphum persicae and Macrosiphum 
solanifolii were removed from them and placed on healthy spinach 
plants growing in a field cage. The blighted plants were then placed 
in another field cage, care being taken not to allow them to come in 
contact with the seedlings nor to scatter any of the remaining aphids 
on the seedlings. A similar cage of field plants served as a control. 
Sixty-three days after inoculation, blighted plants were observed in both 
erf the above cages, while the control plants remained healthy. These 
results indicate that the aphids served as carriers of the blight virus, it 
making little difference whether they were placed directly on the healthy 
plants or allowed to travel by themselves from the blighted plants to the 
healthy seedlings. Mottled leaves were removed from blighted plants 
22 days after the disease had been first observed in the cages, and seven 
plants growing in two pots in the greenhouse were inoculated by mashing 
the diseased tissues into the healthy leaves of the seedlings. A similar 
pot of plants pricked with a flamed needle served as a control. Eight 
days after inoculation two of the plants had developed the mottled leaves 
characteristic of blight, while the five others appeared doubtful. Thirty- 
eight days after inoculation all seven of the plants had developed typical 
symptoms of blight, but the control plants remained healthy. 
Similar results were obtained by inoculating potted plants in the 
greenhouse with a leaf from a blighted plant from the other field cage. 
These results indicate that the aphids carried the blight virus from the 
original field plants to the caged plants and that this virus was readily 
carried from a blighted, caged plant to the greenhouse plants by needle 
pricks. 
Farm E. —On October 21, 1916, spinach seed was planted on a field 
where spinach had not been grown for some time. A characteristic large 
blighted area subsequently developed at one side of this field. On Janu- 
