July i 4f 1923 
Degeneration Diseases of Irish Potatoes 
9i 
leaves of this length were inoculated, and these were so thin they could 
not be bruised as much as is necessary for the successful inoculation of 
potatoes. They were somewhat mutilated with the finger nails and 
by pinching, with juice present on the fingers and applied after mutilation. 
One of this series became mosaic (PI. 15, D). 
Series 4 
Healthy controls to Series 3, with each of five plants in as many pots, 
were inoculated similarly with juice from healthy potato plants. No 
mosaic symptoms appeared by April 26. 
Series 5 
Three untreated controls were transplanted and 13 were not. All 
remained healthy throughout the experiment. 
The five preceding series indicate that potato mild mosaic virus is 
infectious to a high degree when introduced by aphids, and to a slight 
extent when introduced by leaf mutilation, to nightshade. Return 
inoculations from mosaic nightshade plants to potatoes were made to 
sprouted tubers in the same manner as in the tobacco-potato Series 7 
and 8 of Table XXI. It will be remembered that in the control Series 
8, aphids from mosaic potato plants infected 71 per cent of the half¬ 
tubers. The 29 per cent of Series 8 that remained healthy were fed 
upon by fewer aphids than the rest of the series, only 30 being introduced 
to a half tuber. Two series were involved with nightshade and sprouted 
potato tubers, as described in the following paragraph. 
Series 6 
Spinach aphids on mosaic nightshade plants were not very numerous. 
Those present were on the plant of pot 8, Table XXIII, under a cage, 
and were established there on April 6 as a proved nonvirulent colony 
from radish plants. Fifteen or 20 were transferred to each of five 
sprouted half-tubers and 20 per cent of the half-tubers^ became mosaic. 
Thus mosaic was transmitted from nightshade to potato tubers by fewer 
aphids than were required to transmit it from mosaic potato vines k 
Series 7 
Healthy controls to Series 6 were fed upon by aphids from healthy 
nightshade plants, which produced no infection. 
Series 6 and 7 indicate that if enough aphids are transferred to potato 
from mosaic nightshade, infected from potato, there will be as much 
infection as when they are transferred from mosaic potato. 
The experiments with nightshade and tobacco were performed in the 
same greenhouse but in different rooms. Since tobacco mosaic can be 
transmitted to nightshade (2, p. 10) it was slightly possible that the 
mosaic nightshade plants had become infected in some way from mosaic 
tobacco. Therefore spinach aphids were transferred from a mosaic 
nightshade plant to small tobacco seedlings, on April 6. The aphids fed 
and increased until April 26, but all the tobacco seedlings remained 
healthy. 
48108—23-4 
