92 
Journal of Agricultural Research 
Vol. XXV, No. a 
POTATOES AND PLANTS IN DIFFERENT FAMILIES 
Transmission of mosaic from cucumbers (Cucumis sativus L-) to pota¬ 
toes has been reported by Doolittle and Walker (it). The mosaic of 
cucurbits seems to be the most virulent type known and to be the type 
most easily transmitted from one family of hosts to another. However, 
as in northeastern Maine, where potato mosaic is common, the writers 
have not yet found any wild members of the Solanaceae, it has been 
necessary to consider the possibility of transmission of potato mosaic 
between families in connection with the problem of perpetuation in 
weeds. In this region the writers have observed mosaic in garden beans 
(Phaseolus vulgaris T-), evidently introduced in the seed. A very com¬ 
mon mosaic is that of the numerous wild red raspberries (Rubus sp.). 
A mosaiclike disease is sometimes common on certain composites and 
resembles one type of aster yellows. The raspberry mosaic is the only 
one of these diseases that has been tested by the writers in regard to 
transmissibility to potatoes. 
POTATO AND RASPBERRY 
In the Orono greenhouse in the winter of 1920-21, cultivated mosaic 
raspberry bushes were transplanted in October and grown until the 
period of dormancy was passed. On January 28, the new shoots were 
ground up and juice obtained consisting of distilled water and what 
could be washed and squeezed out of the rather dry pulp into the water. 
The juice was used in leaf-mutilation and capillary-tube inoculations 
corresponding to those described in Table XIX, where potato mosaic 
was transmitted. Each method was used in four hills taken, respectively, 
from four 4-hill tuber units. The 16 plants in these tuber units were 
all healthy, as were also the 50 plants of the second generation. This 
indicates that two methods of inoculation that transmitted mosaic from 
potato to potato, were not effective in transmitting mosaic from raspberry 
to potato. No aphids abundant in northeastern Maine are known to 
infest both Rubus and potato (57), which might explain why proximity 
of healthy potatoes to mosaic raspberry has caused no apparent infection. 
CONTROL OF DEGENERATION DISEASES OF POTATOES 
The desirability of controlling any one or more of the degeneration 
diseases depends upon the effect on the yield rate and on the quality. 
The determination of such effects requires correct diagnosis of the disease 
or diseases involved. With a given disease, distinction should be made 
between hills or plots with current-season infection (usually no symptoms) 
with second-season infection (usually first-season symptoms) and with 
third-season infection (PI. 14, B). Until it is clearly shown that disease- 
free strains (stocks of the same variety recently secured from different 
sources) have no inherent differences that survive growth and the produc¬ 
tion of seed in the same environment, it is also desirable to compare 
effects of a disease in parts of the same strain. It may be readily seen 
that it is difficult to secure an extensive comparison fulfilling the pre¬ 
ceding requirements and giving due consideration to soil, variety, and 
climate or season, especially when infectious diseases are present to 
contaminate the healthy parts of strains. Further, the total percentage 
of incidence may affect the average reduction of yield rate by each per 
cent of diseased hills, and diseases in combination may have an effect 
