Bui. 903, U. S. Dept. of Agriculture, 
Plate VI 
Fig. 1. — Pit with reariru 
>s to preserve sarc. 
Temperature as in lLce depth of soil. 
Fig. 2. — Galvanized tin cans used in connection with studies of the underground diffusion of 
Phvlloxera. 
The Grape Phylloxera in California 
