July i, 1918 
True Nature of Spinach-Blight 
23 
and may be readily transferred from the field to the greenhouse, and 
vice versa, by means of the virus causing this disease. 
Blighted plants from the Station field were transplanted to pots of 
greenhouse soil and placed in cages. About these were placed pots of 
seedling spinach. Care was used that the leaves of the seedlings did not 
come in contact with the blighted plants. The next day it was observed 
that aphids had crawled from the blighted plants to the seedlings. 
Thirteen days later definite symptoms of blight were observed on these 
plants. These data indicate that aphids on the blighted field plants 
served as carriers of the blight to the seedlings and that the spinach- 
blight in the Station field was the same as that which had appeared in 
the fields on other farms. 
To prove that the aphids serve as carriers of the virus and not as the 
cause of the blight, mottled leaves from the smaller of the above trans¬ 
planted, blighted, field plants were used to inoculate four pots of spinach 
seedlings by mashing the blighted tissues into the leaves of the seedlings. 
Two similar pots of seedlings were pricked with a flamed needle to serve 
as controls. Eight days after inoculation seedling plants in all four of 
the above pots had developed mottled leaves characteristic of blight, 
especially about the points of inoculation. Thirteen days after inocula¬ 
tion the majority of these plants had developed typical symptoms of 
blight. Twenty-six days after inoculation practically all of the inocu¬ 
lated plants were in advanced stages of spinach-blight, while the controls 
remained healthy. 
Blighted plants were collected from the Station field and brought to 
the laboratory, where aphids were allowed to crawl from them to a pot 
of 50 or more healthy seedlings. The next day it was observed that 
numerous aphids were present on the seedlings. Therefore the blighted 
plants were removed from the cage. Twenty-one days after inoculation 
some of the plants in this pot of seedlings had developed the mottled 
leaves characteristic of blight. Five days later a majority of the 50 or 
more plants developed typical symptoms of blight. The aphids orig¬ 
inally transferred to this pot were killed by fumigation 31 days after 
inoculation. Rhopatosiphum persicae known to be free from infection 
were transferred to these plants. Numerous seedling plants were coming 
up in this pot from seed planted after the original aphids had been killed. 
The majority of these secondary seedlings eventually blighted, thus 
indicating that the aphids had become virus bearers and had transferred 
the inciting entity to the seedlings. 
Ten days after transferring the Rhopatosiphum persicae to the above 
pot of seedlings, a blighted leaf bearing both larval and adult aphids 
was removed from one of the plants and placed on a large plant in a field 
cage. Numerous spinach seedlings from seed planted somewhat later 
were growing about this plant. Thirty-two days after inoculation the 
large plants and two of the seedlings had developed positive symptoms 
