THE GRAPE PHYLLOXERA IN CALIFORNIA. 19 
very frequently spreads along the shorter 8-foot rows, indicating 
that the insects traverse more easily the shorter than the longer dis- 
tances. Aerial and subterranean migrations of wandering larvae 
play an important part in the enlargement of phylloxera " spots." 
Only an infinitesimal percentage of the thousands of wandering 
larvae succeed in reaching their goal, but, as they are parthenogenetic 
radicicoles, a single larva can cause a new infestation or start a 
new " spot " at quite a distance from the original one, either in the 
same or in another vineyard. 
The estimation of root injury from external appearance usually 
can be made with considerable accuracy, and the degree of infesta- 
tion of a vineyard computed by the number of "spots," their size, 
and the stunted condition of the vines composing them. 
The diagrams (figs. 2 and 3) indicate a phylloxera " spot" charted, 
respectively, in the years 1914 and 1915. This " spot " occurred on a 
heavy black clay soil on a hillside of moderate slope. It appeared 
that the " spot " started about the year 1907 when the vines were 3 
years old, and that the first vines died about 1911. Surveys of the 
" spot " were made October 13, 1914, and November 5, 1915, and the 
vines were designated in the following manner: Ten was given to 
vines which showed no external evidences of phylloxeration ; 9 to 
those which showed very slight evidence, such as premature yellow- 
ing of foliage and slight shortening of canes; 8 to those showing 
more advanced symptoms of phylloxeration, and so on down to 1, 
which was given to vines which showed only the most feeble vegeta- 
tive growth. In order to portray the " spot " more vividly, symbols 
have been utilized as follows : Healthy vines, H ; vines designated 9 
and 8, 8 ; vines designated 7 and 6, / ; vines designated 5 and 4, U ; 
vines designated 3, 2, and 1, D ; vines killed by phylloxera, solid dot. 
In this vineyard every fourth vine had been replaced by a walnut tree, 
and these places where vines have been pulled out and not replaced 
are left blank in the diagrams. 
In the diagrams not all the " spot " is shown, for it has extensions, 
the principal one being on the north side across a 24-foot avenue and 
continuing down a swale for some 60 feet. Enough of the " spot " 
is shown to indicate its general form. Between 1914 and 1915 there 
occurred an unusually wet winter and the " spot " grew considerably 
in the 12 months between the surveys. Although the number of dead 
vines increased only from 43 to 49, and among the badly stunted 
types not much increase was shown, there was a marked increase in 
the number of vines showing recent phylloxeration. 
When more than one variety of vine is included in a "spot," a 
good index of the resisting power of the several vinifera varieties 
frequently is observable. Among the dead or moribund vines of 
