178 Bugs, Cicadas, Aphids, and Scale-insects 
the female go directly to the root and produce offspring which are in¬ 
distinguishable from the root form produced in the normal cycle. For 
how many generations the root form can exist and reproduce without the 
invigoration supposed to come from the production of the sexual form is 
not known, but certainly for four years and probably for more. The 
Fig. 249.—Roots and rootlets of grape-vine infested by the phylloxera. (After Ritter 
and Rubsaamen; enlarged.) 
gall form on American vines can be prevented by spraying the vines in 
winter with liquids to kill the winter eggs; but this treatment has no 
effect on the root forms, which in California hibernate abundantly in the 
soil.” 
All forms of the phylloxera species are very small, about of an inch 
being an average for fully developed individuals. The root form is light 
greenish yellow in summer, when it can be found by examining the rootlets 
of infested vines, and bronzy purplish in winter, when it can be found in 
little patches under the bark just at the crown of the vine. The newly 
