AN anatomist's VIEW OF VIRUS DISEASES 87 



eventually through possible changes in the prevailing direction of food move- 

 ment. 



Bennett (1934) has furnished also a clear-cut evidence that the phloem 



Fig. 11. Translocation of curly top virus in a sugar-beet plant with three crowns. 

 Crown I was inoculated with the virus and developed symptoms. Crown II was 

 shaded but not inoculated. It also developed symptoms. In the absence of light 

 it did not form food and received its supply of food from the root. Virus appeared 

 to have entered crown II from the root. Crown III was not treated in any way. 

 It remained free of symptoms during the experiment. Arrows indicate prevailing 

 direction of movement of food. (From an original by Milton Shenkojsky.) 



tissue is actually concerned with the transport of the curly top virus. A par- 

 ticularly instructive experiment was carried out with tobacco plants. Nicotiana 

 glauca, a species of tobacco that upon inoculation with the curly top virus 

 does not develop the symptoms of the disease (a symptomless carrier), was 

 used as a stock for two scions of A^. tabacum, a species highly susceptible to 

 curly top. One scion was placed below, the other above on the stock (fig. 12 



