THE GRAPE PHYLLOXERA IIST CALIFORNIA. 117 



practice to use the same boxes many times in the picking season, 

 and the same boxes may be used in more than one vineyard or dis- 

 trict. In California, wine grapes are rarely picked before the middle 

 of September, and raisin grapes are picked toward the end of August. 

 In the experimental wine-grape vineyard, wandering larvas were not 

 found issuing after August 25, but in young vines in pots they were 

 collected well into September. The fact that the wanderers were 

 not found issuing in the wine grape vineyard at the time when picking 

 boxes were distributed to a certain extent invalidates the theory of 

 spread by these boxes. It is within the realm of possibility, however, 

 that the latest issuing wanderers remained active and alive until the 

 boxes were distributed some two weeks later. Observations on wan- 

 derers issuing from potted vines lead to the conclusion that the natural 

 period of wanderer issuance may be considerably lengthened beyond 

 that which was found to obtain in the experimental vineyard during 

 the years 1914 and 1915. This longer period would include the time 

 of picking wine as well as raisin grapes. 



PLANTS BETWEEN THE VINES. 



Walnut trees planted in vineyards indicate the possibility of 

 diffusion through the agency of plants. The long roots of the 

 walnut offer facilities for phylloxeras to spread whenever vine 

 roots come in contact with them or are very close to them. That 

 phylloxera? have been found moving on these roots would indicate 

 that the latter often provide an underground channel of diffusion. 



MAN AND DOMESTIC ANIMALS. 



The possibility of the portage of phylloxeras by man and do- 

 mestic animals should not be overlooked. The winged forms and 

 aerial wanderers may be blown on clothes or animals, and thereby 

 spread, or they may be picked up with wet earth. This latter chance 

 is greatly lessened under California conditions, because during the 

 months in which wanderers and winged migrants are produced, 

 the surface soil is dry, and the winged migrant is not a factor in 

 diffusion. 



Eecognizing the possibility of the spread of phylloxeras through the 

 agency of flowing water, the writers conducted the following experi- 

 ments in 1911: From May 5, 11 a. m., to May 6, 11 a. m., a piece of 

 severed root, infested by six adult overwintered phylloxeras and about 

 100 eggs and larvas, was subjected to a stream of water for the most 

 part playing directly upon the insects and flowing 6 feet to an unin- 

 fested vine (Catawba) so as to effect contact with some of its roots and 



