THE GRAPE PHYLLOXERA IN CALIFORNIA. 105 



trunk is considered as the central point. On two occasions wan- 

 derers were caught on paper placed equidistant (5 feet) from four 

 trunks of infested vines. Examinations showed that between one 

 vine and another, even of apparently equal phylloxeration, a great 

 variation in the production of wanderers took place. It also ap- 

 peared that there Was a tendency to produce these forms all at one 

 time as though they had collected in a mass and then issued all to- 

 gether. As regards the time of day at which they were most abund- 

 ant, it appeared that more might be observed between 10 a. m. 11 and 

 1 p. m. than at other daylight hours. European observers found 

 that in general the wandering larvae appeared in greatest abundance 

 in the early afternoon, which is the hottest part of the day. 



Vineyard observations were continued in 1915. The same vine- 

 yard was used, but more attention was paid to phylloxerated vines 

 on the parts in which the soil was a heavy black clay. On 

 this heavy soil no wanderers appeared before July 24, and none 

 was found after July 29. The larva? also were always very scarce, 

 notwithstanding the fact that the soil contained numerous cracks 

 which would enable the wanderers to reach the surface. On the 

 lighter soil (clay loam), wandering larvae first appeared July 14, 

 and they continued to issue until August 18. During this period 

 of over a month about two-thirds of the phylloxerated vines exam- 

 ined were producing wanderers. Between July 15 and 21 they 

 were most abundant, as many as 20 or 30 living individuals being 

 visible at one time beside the more heavily infested vines. In 

 August hundreds of dead larva? could be seen on the surface of the 

 soil around the bases of the vine trunks, and large numbers were 

 caught in spider webs. As in the previous year, the vines bearing 

 the largest numbers of wanderers were those of recent phylloxeration. 



In 1915, during the period of wanderer activities, the weather was 

 for the most part quite hot and dry. Occasionally there were cool 

 days, and on these the wanderers appeared to be as active as on the 

 hot days. 



It appeared certain that the great majority of the wandering larva? 

 ascended to the light by way of the main trunk of the vines, around 

 which there occurred almost always a wide crack. More issued from 

 Zinfandel vines than from Carignan vines equally phylloxerated, 

 perhaps because the Zinfandel had thrown out more fleshy rootlets in 

 May and June, and these had decayed in July while heavily infested. 

 It would thus appear that many of the wandering larva? are pro- 

 duced on these surface fleshy rootlets and leave them because they 

 have become overcrowded or have started to decay. 



In each of the years 1914 and 1915 wandering larva? appeared in 

 the vineyard over the same period, i. e., from the middle of July to 



11 All references to clock time refer to " Standard time." 



