Jtily i, 1918 
True Nature of Spinach-Blight 
41 
were given no food. The individuals which had molted and become 
adults in the vials were transferred to healthy plants. Forty of M. 
sokmifolii were placed on 20 healthy spinach plants on which they were 
allowed to remain for 48 hours. Six of the plants developed positive 
symptoms of the disease in an average time of 24.3 days. Forty of R. 
persicae were transferred to 20 spinach plants for a period of 48 hours. 
Four plants became infected and the symptoms appeared in an average 
time of 25.2 days. From these results it appears that when molting occurs 
after an aphid has left a diseased plant the insect may even then be able 
to produce infections of blight in healthy plants upon which it feeds, and 
indicates that the virus is transmitted in some other manner than on 
the external appendages of the insect's body. 
ability of offspring of virus-bearing aphids to carry infection 
A series of healthy plants were inoculated by transferring to them at 
the time of birth the offspring of virus-bearing aphids. The young aphids 
had neither been allowed to feed previous to their transference to healthy 
plants; nor had they in any way come in direct contact with spinach 
affected with the disease. A number of adult female virus-bearing aphids 
were transferred directly to healthy spinach plants. The offspring of 
these females were transferred to the experimental plants as soon as they 
were bom. Fifty of the immature Macrosiphum solanifolii were trans¬ 
ferred to 25 healthy spinach plants and allowed to remain on them for a 
period of four days. They were then destroyed by fumigation. One 
plant became infected, and positive symptoms of blight appeared on the 
twenty-eighth day. As the young aphids had not taken food previous to 
their transference nor had any association with diseased plants before 
being placed on the healthy seedlings, the infections obtained of blight 
indicated that the young became associated with the infectious entity 
previous to their birth. 
transmission of the infectious entity of blight by adult virus¬ 
bearing APHIDS TO THEIR OFFSPRING 
The results obtained in the earlier experiments on the insect trans¬ 
mission of spinach-blight indicated the possibility that the inciting factor 
of the disease was transmissible by a parent aphid to its offspring, thereby 
rendering the latter capable of producing infections in healthy spinach, 
although they had not previously fed on a diseased plant. The following 
experiments were performed to obtain data relative to this point. Both 
species of aphids were used and consisted of the Virginia, Alabama, and 
Louisiana strains previously discussed. The strains were confined in 
separate cages and were pure. On the same day the various lots of 
aphids were placed on fourth-stage-diseased plants in which the disease 
had been produced by virus inoculations made 42 days previously. The 
