34 BULLETIN 879, U. S. DEPARTMENT OF AGRICULTURE. 
ROOT INOCULATIONS. 
Attempts to produce mosaic by inoculations through the roots 
have so far given negative results. Seventy-four plants have been 
inoculated, using the following three methods : 
(1) Inoculation of the roots was made with the expressed juice of a mosaic plant 
or by the insertion of crushed fragments of mosaic leaves in wounds in the larger roots 
at a distance of 1 to 6 inches from the stem. 
(2) Mosaic vines were passed through a food chopper and the ground material mixed 
with sterilized soil. Healthy plants were then transplanted in the soil thus prepared, 
the process of transplanting insuring root injuries as points of possible infection. 
(3) Roots of healthy plants were injured at points close to the surface of the soil, 
and the expressed juice of mosaic plants was then poured about the stem close to the 
point of injury. 
No infection has resulted from any of these methods, and the dis- 
ease apparently is not transmitted through the roots. 
RELATION OF AGE AND VIGOR OF PLANT GROWTH TO SUSCEPTIBILITY. 
t 
The percentage of successful inoculations on the cucumber and 
other curcurbits seems to be directly related to the age of the plant 
and the vigor of its growth. Inoculations on seedling plants, even 
up to the time that three or four leaves have appeared, give a low 
percentage of infection, and it is especially difficult to secure infec- 
tion on seedlings during the development of the first true leaf. 
A little later, however, when the plants begin to grow rapidly and 
have developed six to eight leaves, most of those inoculated develop 
the disease. This period of susceptibility then continues until the 
plant becomes old and growth has nearly ceased, at which stage the 
percentage of successful inoculations again becomes low. Plants 
growing under unfavorable conditions which cause a stunting or 
retardation of growth are also less susceptible to the disease and show a* 
the first symptoms more slowly than those which are growing rapidly. 
These facts indicate that the age and vigor of the plant have a 
direct relation to its susceptibility to mosaic. While this is probably 
true, it is a question what relation these factors bear to the suscep- 
tibility of the plant and its response to the disease stimulus. The 
rapidly dividing cells of the tissues still in the process of development 
apparently react to the disease stimulus more readily than the older 
tissues. It is possible that these younger tissues offer conditions 
more favorable to the multiplication of the virus 1 and consequent 
infection than the older cells of mature plants. 
It has been suggested that older plants may contain the virus but |- 
show the symptoms in so mild a form that they can not be detected. 
However, this has apparently been disproved by making inocu- 
lations from old plants which had been previously inoculated with 
i The term virus is used here in the commonly accepted sense of the infective agent of a disease with which 
no visible organism has been associated. 
