THE GRAPE PHYLLOXERA IN CALIFORNIA. 123 
of that industry and, it is estimated, has in the course of some 60 
years destroyed about 75,000 acres of grapes. 
In many instances the insect has been distributed through the 
agency of infested rooted vines imported into an uninfested district 
or vineyard. In other cases the insect has been carried on vineyard 
material. In no instance has the distribution been as rapid as that 
which took place in the vineyard districts of France. The modi- 
fied life cycle in California, i. e., sterility of the winged form, 
coupled with topographic barriers, consisting of mountain chains and 
dividing valleys, is in very great part responsible for this. 
VINEYARD DESTRUCTION. 
There is great variation in the rapidity of the destruction of vines 
and vineyards by phylloxera. 
Apart from some variation in the different grape varieties, soil 
conditions must be considered as of great importance. In poorly 
drained soils the vines succumb much more rapidly than in well- 
drained land. Accumulation of moisture in the subsoil materially 
assists in the decomposition of infested roots, whereas if the subsoil 
is well drained, vines may flourish notwithstanding infestations ex- 
tending over many years. Vines attacked when young and before 
their root systems have become established will succumb more rapidly 
than will those infested at a greater age. 
The first indication of phylloxera in a vineyard occurs in the form 
of one or more stunted vines and a premature yellowing of the 
foliage. In time, adjacent vines will show similar indications, and 
those first infested are more noticeably stunted. Gradually more and 
more of the surrounding vines are affected, and those in the center 
become very much weakened or die outright. Thus are formed the 
so-called " oil spots " or foci for the distribution of the disease, which 
may be likened to the ever-increasing concentric circles of waves that 
are formed when a stone is cast into placid water. 
Following the initial infestation of a vine under favorable condi- 
tions for phylloxera, the insects multiply rapidly, and within two 
or three years increase their range to involve the entire root system. 
Those which settle on the growing rootlets form fleshy lesions or 
swellings, which are termed nodosities. These swellings are gener- 
ally somewhat curved, the insect inhabiting a depression of the inner 
arc. In the great majority of instances the insect stops further apical 
growth of the rootlet, and thus the rootlet ceases to supply nourish- 
ment to the vine. Although the percentage of rootlets thus infested 
is often large, a vine of vigor can easily send out more and continue 
to draw its nourishment from the soil. Other phylloxeras settle on 
the older roots and in most cases cause swellings termed tuberosities, 
