Bui. 903, U. S. Dept. of Agriculture. 



Plate VI. 



Fig. 1. — Pit vrith rearms boxes, illustrating method of covering with quilted strips to preserve same 

 temperature as in like depth of soil. 



Fig. 2. — Galvanized tin cans used in connection with studies oi the underground diffusion of 



Phylloxera. 



The Grape Phylloxera in California. 



