566 S, E. LURIA 



we happen to observe it. A great deal of independent, divergent evolution 

 may have taken place both in virus and in cells since a virus first arose from 

 a cell constituent through the acquisition of an apparatus for successful 

 transfer from ceU to cell. Conceivably, most cells may have great latitude in 

 the variety of genetic elements, exogenous or endogenous, whose reproduc- 

 tion they are potentially capable of supporting. Only those elements that have 

 evolved both a mechanism for successful transfer and a set of functions 

 observable in other cells may be recognizable as viruses. Transferability of a 

 virus may be extended by mutation to cells that are phylogenetically very 

 distant from one another and from the (hypothetical) cell whence the virus 

 first came. Suffice it to recall the plant pathogenic viruses that can multiply 

 in the cells of plants and of insects (Mara.morosch, 1955). 



To return to virus multiplication, the hypothesis of a genetic relationship 

 between viruses and cellular organelles does not in. itself contribute to our 

 present understanding of virus multiplication. In fact, we know very little as 

 yet about the mechanism of reproduction of these organelles. Rather, we 

 may be certain that the study of virus multiplication will, directly and in- 

 directly, be a major contributor to the elucidation of the mechanisms of 

 replication of the basic units of life. 



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