140 



C. A. KNIGHT 



because the most extensive and best integrated studies have been made on 

 them. These strains are illustrated in Fig. 1, which shows some of the symp- 

 toms that they cause in one host, Turkish tobacco. The strains shown at the 



TABLE II 

 AarLNO Acid Content of Some Plant Vmus Preparations " 



Constituent 



Virus "" 



TMV 



TMV* 



CV4 



BSV TYMV 



References 



(Gm. amino acid residue/100 gm. virus) 



<* The following abbreviations are used: TMV, tobacco mosaic virus; CV4, cucumber 

 virus 4; BSV, bushy stimt virus; TYMV, turnip yellow mosaic virus. 



'' TMV values from microbiological assay. 



^ TMV values from ion exchange chromatography. 



" Cysteine was determined in the native virus by the method of Tsao and Bailey 

 (1953). 



<* Dash indicates that no analysis was made for the amino acid indicated. 



^ A correction was made in the case of BSV for glycine derived from nucleic acid 

 degradation, but not in the other cases. 



top of Fig. 1 were selected from available ones at the Rockefeller Institute 

 for their distinctive biological properties. Some are closely related to ordinary 

 TMV and others not (Knight, 1947). The strains illustrated at the bottom of 



