.392 
Journal of Agricultural Research 
Vol. VIII, No. io 
with carbol-fuchsin, the xylem fibers stain red and the xylem tubes 
orange, indicating an abnormal condition of the walls of the xylem 
tubes. 
ROOTS 
The diseased spots may be found in the large roots, which when split 
show dark longitudinal lines corresponding to these spots. 
FRUIT 
The effect on the crop has already been noted. On slightly affected 
vines the crop may be diminished considerably. Those at all badly 
affected have a tendency to fail to set their fruit, and much of that which 
does set fails to develop or mature. 
A microscopical examination of the pedicels of diseased bunches shows 
that there is little activity in the cambium. A lack of thickening of the 
pericylic fibers and of the collenchyma is also noted which explains the 
fragility of the stems and failure of the berries to develop (PI. 91, F, G). 
INFECTIOUSNESS 
There is little or nothing in the distribution of the disease to indicate 
an infectious nature. Some growers claim that the infected areas 
gradually enlarge, but they are probably misled by the annual variations 
already noted. It is also possible that vines, so slightly affected at first 
that the injury passes unnoticed, gradually weaken and show the effects 
more plainly later, thus giving the impression of a spread of the trouble. 
In some vineyards the disease has existed in spots for years without 
spreading. Perfectly healthy vines may show symptoms of little-leaf in 
the nufsery and yet develop into perfectly healthy vines when planted in 
another soil. On the other hand, vines which appear healthy in the 
nursery may show the disease the first year when planted in certain soils. 
In the latter case, however, the disease does not usually manifest itself 
until the third or fourth year. 
ETIOLOGY 
No connection has been found between the disease and any vegetable 
or animal organisms. Bacteria have been found in diseased tissues, but 
inoculations in various ways afforded no evidence that they have any 
connection with the disease. 
Young vines showing the disease in affected nurseries have been . 
planted in districts where little-leaf does not occur, and they have de¬ 
veloped normally, showing no symptoms of the disease in the new loca¬ 
tion. On the other hand, healthy vines from an unaffected district may 
show the disease the first year after planting in an affected district. 
Both of these cases are exemplified by direct experiments made at Davis 
