Fig. 18. Eleetix))! 

 micrograph of turnip 

 yellow mosaic virus 

 contrast-stained witli 

 p liosp hot ungstate 

 (magnification: x 

 500,000). Note sug- 

 gestion of substructure 

 and compare with Fit;. 

 17. Electron micro- 

 graph by Dr. S. Brenner 

 and ]\Ir". R. W. Home. 



Fig. 1!>. Tobacco leaf hiocu'ated witli a 

 tobacco necrosis virus. The concentration of 

 virus used for the inoculation is suitable for 

 local lesion counting, but is not sufficient for 

 preparative purposes. 



