CAUSE OF THE DISEASE. 



15 



loosely a covering of chiffon or silk veiling; then over that one 

 of Brussels netting (figs. 4 and 5). The chiffon is impenetrable 

 to the insects, but will not withstand the weather; the Brussels net 



Fig. 4. — Isolation cage and Mason jars for isolating sugar-beet plants. 



is strong, but will exclude nothing smaller than adult leafhoppers; 

 therefore both materials were used together. These covers were 

 drawn well down the sides of the foundation frames and secured 



Fig. 5. — Another type of isolation cage. 



(here by tacking laths over their free margins to the sides of the 

 foundation frame. Special care was taken to make the corners 

 tight. To place insects in the cage a lath was temporarily removed 

 33S01— Bui. 1S1— 10 3 



