148 



C. A. KNIGHT 



b. Summary of Compositions of Strain Nucleic Acids. All plant viruses 

 analyzed so far appear to contain ribonucleic acid. Each different plant virus 



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§5 



3 .; 



has been found to possess a nucleic acid containing characteristic proportions 

 of purine and pyrimidine nucleotides. Thus, the nucleic acids of different 

 plant viruses have demonstrably different compositions. In contrast, variant 



