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 phylloxeras 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 INSTRUMENTS. 



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 phylloxeras. 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 



