352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



the roots of which had given no reaction upon the cowpeas, were 

 selected for a second test. Tliis was made, again to cowpeas, 5 weeks 

 after the first test. The plants were by this time about 8 inches across 

 with a well-developed root system, and showed no unusual symptoms. 

 Of these 48 plants 32 gave a virus reaction. In considering these re- 

 sults certain other facts must be borne in mind ; exhaustive tests make 

 the explanation of outside infection by seed transmission unlikely, 

 though the possibilities of air- and water-transmission, via the soil, 

 cannot be excluded. The virus is not insect borne. 



There seem to be three possible explanations of this problem : first 

 it may be assumed that the virus is present all the time in the stem, 

 but present either in a nonvirulent form which requires to gain 

 virulence by concentration in particular cells of the root, or else in a 

 dilution too great to give a positive reaction on inoculation. This 

 theory, of course, involves seed transmission of the virus in unde- 

 tectable form or quantity. The second possible explanation is that 

 the virus is arising spontaneously within the plant. The third 

 explanation, and perhaps the most likely, is the existence of a mode of 

 virus transmission at present quite unsuspected. 



Virus workers have long dallied with the idea that a virus might 

 arise de novo within the host. Such a suggestion is attractive in 

 some ways and it would explain many things which are at the mo- 

 ment obscure. If viruses are considered as organisms or at least 

 possessing some of the attributes of life, the suggestion of their 

 heterogenesis is repugnant. If, on the other hand, Stanley's view 

 that a virus may be an autocatalytic protein is accepted, then there 

 seems no particular reason why the theory of spontaneous develop- 

 ment of the virus within the host should not also be accepted. It is, 

 however, at present still an open question, and much work remains 

 to be done before this question can be answered. 



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