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



vines planted in lighter soils grew poorly and that the percentage 

 that died was greater than in the case of heavy soils. 



In 1914, wanderers were taken from jars in the laboratory cellar 

 and successfully colonized on pieces of roots. It was found that they 

 developed into the usual type of radicicole phylloxerse. In order to 

 ascertain definitely the future of wanderers observed in the vine- 

 yard a thrifty section of sound grape root was transported to the 

 vineyard on July 17, 1915, and 12 larvae, wandering upon the sur- 

 face of the soil, were placed thereon. Four of these subsequently 

 matured as wingless radicicoles between August 23 and 27, and 

 before the advent of winter a considerable colony was established. 

 A contemporary experiment of similar nature was carried out with 

 a like result with larvse taken wandering on the surface of the soil 

 in pots containing infested vines. 



In conjunction with the inoculation experiment in the vineyard 

 four Zinfandel vines were planted in kerosene cans in the laboratory 

 yard, and after watering to insure soil cracking they were inocu- 

 lated artificially by placing the larvse on the soil surface. These 

 inoculations comprised, respectively, 21, 190, 300, and 625 wanderers 

 collected during the summer. Two of the cans contained sandy silt 

 and two heavy black clay. In no case did infestation result. 



For another experiment two galvanized- iron cans, 4 by 4 inches, 

 and 10 inches deep, were used. Sound pieces of vine root were placed 

 in each, 7 inches below the soil surface, and the cans then filled to the 

 top, one with sandy silt and the other with heavy black loam, after 

 which the cans were buried, their tops at a level with the soil surface. 

 The surfaces were watered to insure cracking of the soil. Between 

 July 15 and August 4, several hundred wanderers were placed on the 

 sandy silt, and between July 18 and August 4 several hundred on the 

 black loam. On August 27 the roots in the cans were examined. 

 Those buried in the sandy silt which had failed to crack much were 

 uninf ested, while those buried in the heavier soil bore a small infesta- 

 tion, indicating that one or more wanderers had penetrated to the 

 roots. 



From the results of experiments on natural and artificial inocula- 

 tions of vine roots by wandering larvae through the soil two facts 

 stand out: (1) Notwithstanding the large numbers of wanderers 

 available or utilized, positive results were infrequent. In the years 

 1913, 1914, and 1915, altogether 14 vessels containing vine roots, 

 either living or cut into sections, were inoculated by placing wander- 

 ers on the soil surface, and only two of these gave positive results. 

 The average number of wanderers used for each vessel was about 150. 

 In the vineyard experiment in 1915, only 4 of 27 exposed vines be- 

 came inoculated, yet all these vines were planted near vineyard vines 



