THE GRAPE PHYLLOXERA IN CALIFORNIA. 113 
from which wanderers were issuing. It is true that the soil surface 
inside the cans was a small area — 126 square inches — and that the 
soil itself was not as thoroughly cracked as it might have been ; but 
in many instances the cans were not more than 1 foot from the 
trunks of the infested vines, therefore, from the wanderers when 
they issued, whereas in vineyards vines are set 6 or more feet apart. 
(2) The presence of cracks in the soil leading directly to roots is 
necessary to permit the wandering larvae to descend to roots, for the 
larvae can not dig their way through the soil, and during the period 
when they are issuing, rain, which might provide moisture to draw 
them into the soil or wash them onto exposed roots, is lacking. 
The writers are of the opinion that wandering larvae are the cause 
of considerable local spread of phylloxera, that is, within the vine- 
yard or district; and that they are instrumental in causing the 
formation of new phylloxera " spots " or foci. Under favorable 
conditions it has been proved that they may live for at least three 
days above the surface of the soil, and thus may be transported 
from place to place with the possibility of finally becoming located 
on a vine root. There is no reason why wanderers may not live for 
as long as two weeks on the soil surface without feeding, provided 
this surface is not heated by the sun. In one instance, after being 
placed on a piece of root, several of them wandered for as many as 
five days before settling down to feed. It may be said also that 
larvae have been found to live in water as long as nine days without 
food, and it may thus be assumed that they might remain as long in 
the open air under average conditions of temperature and humidity. 
This fact would explain how the insect may be spread from one 
locality to another by wandering larvae that lodge in such vine 
material as picking boxes (see following under " Casual agencies of 
diffusion," p. 115). 
There are certain marked instances in California vineyard dis- 
tricts where phylloxeration has developed " with the prevailing 
winds." The only wind-borne forms of the phylloxera in California 
are the winged migrants and the wandering larvae. The California 
biology indicates that the migrant has no bearing on the preserva- 
tion of the species, and therefore such phylloxeration has resulted 
from wind-borne wandering larvae. 
DIFFUSION BY NEWLY HATCHED RADICICOLES TRAVELING THROUGH THE SOIL. 
In 1914, experiments on subterranean diffusion were conducted. 
In April three Muscat rooted vines were planted in a 4-foot square box 
containing heavy loam covered with a 3-inch layer of fine sand. The 
sand was used for the purpose of preventing wandering larvae from 
emerging upon the surface and reaching the sound vines. May 20, 
1900°— 21 8 
