THE GRAPE PHYLLOXERA IN CALIFORNIA. 103 



the rootlets growing in contact with the pot. Experiments showed 

 that when sand was dry it obstructed the wanderings of the phyl- 

 loxera?, but when moistened the phylloxera? might be drawn through it 

 with the water. It was also found that in sandy soils water might 

 occupy all the interstices between the grains of sand, repelling the 

 phylloxera?, whereas in soils of other types air cavities existed suf- 

 ficient to enable the phylloxera? to live. 



In California the wandering larva? were first observed in glass 

 jars in which were kept phylloxerated roots in the summer of 1913. 

 When such jars were removed from the darkness of the cellar to a 

 light room, young larva? were observed wandering up the sides of 

 the jars. In the dark cellar such wandering took place, but after 

 light was admitted to the jar the wandering became much accentu- 

 ated. Similar wandering of larva? was observed in the cages used 

 for observations on living roots (Pis. V, VI, fig. 1; VII). 



Until 1914 no vineyard observations in this direction had been 

 made, but in that year wanderers were observed in their normal 

 state. For these observations, vines in a phylloxera " spot " in a 

 Zinf andel vineyard 10 years old were selected. This " spot " was 

 situated on light clay loam upon sloping ground, and within its 

 confines wandering larva? were observed during July and August. 

 These were found in greatest numbers coming from vines near the 

 outer edge or periphery of the " spot." Such vines had little ex- 

 ternal evidence of phylloxeration, but upon examination it de- 

 veloped that the roots were heavily infested and produced many 

 migrants as well as wanderers. From vines obviously moribund a 

 smaller number of wanderers appeared. Wanderers also were ob- 

 tained on the same horizontal boards with sticky papers on which 

 migrants were caught. These were captured close to the edge of 

 the sticky substance and never farther from it than 6 mm., and it 

 appeared that all those taken had crawled to the papers and that 

 none had been borne on the wind. On vertical papers, not even 

 when placed within 2 feet of the wanderers, and to the leeward of 

 them, were any phylloxera? captured. It was observed, however, 

 that on favorable occasions wanderers are easily borne off by gusts 

 of wind. The part of the vineyard in which wanderer activity oc- 

 curred was moderately well cracked through drying. On the hori- 

 zontal sticky papers wanderers were caught at points from a few 

 inches from the vine trunk to 5 feet from the nearest vine and 

 directly in the center of a square described with a vine at each angle. 

 In this latter case either the phylloxera? had ascended by the trunk 

 of the vines, and then walked 5 feet, or else they had ascended by 

 means of cracks nearer the paper. In either case it is obvious that 

 the spread of a given phylloxera " spot " may result from the activi- 

 ties of these wanderers without the agency of wind. 



