102 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



August 3, 7, 11, 14, 17, 20, 21, 31. Horizontal boards were placed 

 July 10, 13, 21, 24, 31 ; August 7, 11, 14, 17, 21, 25, 31 ; September 

 5, 11, 26. 



On the vertical boards eight migrants were captured between July 

 13 and August 21, and on the horizontal boards, between July 10 and 

 August 17, 51 were taken. The area of paper exposed on the vertical 

 boards was 63,725 square inches, almost 50 square yards, while that 

 of the horizontal boards was 7,625 square inches, not quite 6 square 

 yards. The papers kept sticky for about four days on the average. 

 Considering the comparatively large number of migrants captured 

 on the limited areas of sticky paper, there must have been a 

 heavy infestation throughout the vineyard. Winged phylloxera? were 

 observed on and about the bases of vine trunks, and many were 

 caught in spider webs and died. Whether the migrants deposit the 

 sexual eggs in the vineyard or not, the total absence of galls on 

 the vines (vinifera? and resistants) surely indicates that such eggs 

 come to nought. 



From rather meager observations it appears that the sexuals require 

 a high temperature, coupled with considerable humidity, for their 

 successful development, and that the climatic conditions of Califor- 

 nia lack the requisite combination. 



DIFFUSION BY NEWLY HATCHED RADICICOLES ISSUING FROM THE SOIL. 



In the summer of 1868, Faucon, in France, observed young radici- 

 coles wandering over the surface of the soil following a heavy rain, 

 which had caused the soil to crack open in drying. He also observed 

 the phylloxera? to enter cracks and disappear. In 1872, he again 

 observed these phenomena between August 4 and September 30. The 

 year following, his observations were made from June 14 to Septem- 

 ber 13, so that he was able to see wandering larva? during a period of 

 three months. In 1876, Boiteau, m France, confirmed the observa- 

 tions of Faucon, adding that he found that the greatest number of 

 wanderers issued from vines at the periphery of the phylloxera 

 " spot." Since then other observers have discussed the phenomenon 

 of "wanderer" diffusion. Grassi (11, p. 351, 138, 148) and his col- 

 leagues, working from 1907 to 1911, conducted a series of experiments 

 with the wandering larva?. They found that these were strongly 

 attracted to light and that in walking over the soil surface they did 

 not go in a straight line, but deviated according to the variations of 

 the surface. On a piece of glass they proceeded in a straight line and 

 covered a distance of about 2 cm. the first minute. 



As regards inoculation of vines by these wandering young, suc- 

 cessful experiments were carried out in Europe on vines in pots, it 

 being found that the wanderers penetrated the cracks formed be- 

 tween the inside periphery of the pot and the drying soil and infested 



