THE GRAPE PHYLLOXERA IN CALIFORNIA. 115 
radicicoles in all stages and with a few nymphs, indicating that the 
original infestation occurred at least before August 1. The vine at 
the end of the 10-foot tube was uninfested and showed no indications 
of ever having been inoculated. 
On May 22 a similar experiment, with single vines (Carignan), 
was started, the length of the wooden tubes being 6 and 14 feet, re- 
spectively. On September 30 the vines were examined and the roots 
of the central vines were found to be well infested. Rootlets of all 
four vines had penetrated not over 3 inches into the hollow interior 
of the tubes. The vine 6 feet distant from the infested vines showed 
a good infestation, whereas the vine 14 feet away was not infested. 
Thus, wandering larvae, in two cases out of four, had found their 
way along the whole length of the interior of the tubes and had 
inoculated the roots at the farther ends of such tubes. The inocu- 
lated vines were those at the ends of the two shorter tubes (2 and 6 
feet), and the sound vines those at the ends of the two longer tubes 
(10 and 14 feet). Thus it would appear that there is a limit to the 
distance over which the phylloxera? will proceed when they have left 
a root, intent on finding new food. These experiments with wooden 
tubes demonstrated the wandering habits of the young radicicoles, 
and it may be readily understood how this subterranean movement 
may cause a phylloxera " spot " to enlarge, especially when the soil 
is cracked to any depth. 
DIFFUSION BY YOUNG GALLICOLES. 
In districts where the gall-inhabiting forms (gallicoles) are found, 
they may be the cause of diffusion. Either the branches of vines 
intertwine and the young gallicoles pass thus from one vine to 
another, or the young gallicoles are carried by the wind on to foliage 
of other vines or to the ground. Since the gall-inhabiting form is 
normally absent in California, this means of diffusion will not be 
discussed* further. 
CASUAL AGENCIES OF DIFFUSION. 
CULTIVATING INSTKUMENTS. 
During May and June badly phylloxerated vines are accustomed 
to put forth an abundance of short fleshy or fibrous rootlets close to 
the surface of the soil. Usually these are infested heavily with the 
progeny of the overwintered phylloxera?. The vineyards usually are 
cultivated and hoed at this time, and these surface rootlets are fre- 
quently broken off and carried along by the cultivator and hoe. 
This possible means for spreading the insect having been considered, 
a series of experiments was initiated as follows : On May 30, in the 
vineyard, pieces of infested fleshy surface rootlets were secured, 
placed in earth, and the whole transported to the laboratory. Four 
