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 Riibsaamen; 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 



