THE MOSAIC DISEASE OF CUCURBITS. 37 
VIRUS IN THE ROOTS. 
Inoculations from the roots of mosaic plants have so far given 
negative results, and it is doubtful whether the virus is present in 
these parts as in the remainder of the plant. Allard (1) notes that 
the roots of mosaic tobacco plants contain the virus in many cases. 
In the case of cucumber mosaic, inoculations have been made from 
the roots of plants of various ages, using either the expressed juice of 
the root tissues or crushed fragments of the tissues themselves. 
Inoculations have been made into the stems, leaves, or roots of 58 
plants, but no infection has occurred. 
\IRUS DISTRIBUTION IN THE PLANT. 
RAPIDITY OF SPREAD OF THE VIRUS. 
In all inoculations with cucurbit mosaic the earliest signs of infec- 
tion appear in the youngest leaves. This is also the case with to- 
bacco mosaic and other diseases of this type, the leaves which are in 
process of development seeming to respond most rapidly to the 
disease stimulus. The time required for the development of these 
symptoms is usually the same, regardless of the point of inoculation, 
indicating that the virus is rapidly distributed to all parts of the 
plant. The youngest leaves of the cucumber develop mosaic symp- 
toms as rapidly when inoculation is made at the base of the stem as 
when made in the leaf itself. This does not prove that the virus is im- 
mediately distributed throughout the plant, however, for the infective 
principle is present in the cells for some time before visible symptoms 
occur and it is probable that the virus is present in greater amount 
near the point of inoculation for at least a short time after inocula- 
tion. The older leaves, however, do not show definite signs of the 
disease for some time, and no external indication of the disease ap- 
pears until the young^ leaves develop mosaic symptoms. The accu- 
mulation of the viri*s at the point of inoculation earlier than at the 
growing tip has been demonstrated in large cucumber plants where 
inoculation was made at the base of the stem about 3 inches below 
a small lateral shoot which was 6 inches in length. The leaves of 
such a shoot showed the symptoms of the disease 12 hours before it 
appeared in the young leaves at the tip of the main runner, which 
were 30 inches beyond the point of inoculation. This occurs occa- 
sionally in large vines, but in most cases there is no appreciable dif- 
ference in time between the development of symptoms at various 
points, and the distribution of the virus through the plant must be 
comparatively rapid. 
Experiments have shown that the juice of an inoculated plant 
may be infectious 18 to 48 hours previous to the appearance of any 
definite mosaic symptoms and also, as already indicated, that the 
juice from leaves near the point of inoculation may become infec- 
