SECTIONAL TRANSACTIONS— K. 503 



Mr. F. C. Bawden. — The isolation and properties of some plant 

 viruses (ii.o). 

 Tobacco mosaic virus, cucumber virus 3, potato virus X and Bushy 

 stunt virus have been isolated and found to be nucleoproteins. The 

 analytical figures are all similar except that Bushy stunt virus contains twice 

 as much nucleic acid as the others, and the apparent absence of water and 

 any constituents other than nucleic acid and protein sharply separates 

 these viruses from bacteria and other organisms. Tobacco mosaic virus, 

 cucumber virus 3 and potato virus X have rod-shaped particles ; they form 

 birefringent gels, dilute solutions show anisotropy of flow and concentrated 

 solutions are liquid crystalline. Precipitates of the first two with acid or 

 ammonium sulphate are paracrystalline, but those of potato virus X are 

 amorphous. The particles of Bushy stunt virus are spherical and all 

 preparations of this virus are isotropic ; when precipitated with ammonium 

 sulphate at 0° c. it forms true cubic system crystals. The proteins are 

 infective at dilutions of from 10* to 10 " and give serological titres of 

 from 10-* to 10-'. The type of specific precipitate with antisenmi varies 

 with the shape of the virus particles. The rod-shaped viruses give floccu- 

 lent precipitates similar to those of bacterial flagellar antigens, whereas 

 Bushy stunt virus gives a dense precipitate similar to those given by bacterial 

 somatic antigens. 



Dr. R. W. G. Dennis.— r/te virus content of some Peruvian potatoes 

 (11.30). 



In December 1937 a consignment of fifty-nine Peruvian potato varieties, 

 collected at Puno by the Percy Sladen Expedition to Lake Titicaca, was 

 received at the Potato Virus Research Station Cambridge. During the 

 present season their virus content has been under investigation by the 

 writer. The virus most frequently isolated is X, which is present in thirty- 

 four varieties ; several strains occur, some of which are carried without 

 symptoms by tobacco whilst others induce an interveinal mottle with 

 yellow rings. A necrotic or ringspot type capable of inducing local lesions 

 on tobacco or Datura has never been isolated. One variety has yielded an 

 X the symptoms of which on European potatoes recall those of Foliar 

 Necrosis, virus D. Associated with X in at least nine varieties is a ' streak ' 

 virus probably identical with Up To Date Streak, virus B. 



Nine other varieties contain viruses of the Aucuba Mosaic type. It is 

 probable that these mostly resemble the virus of Tuber Blotch (F) rather 

 than true Aucuba (G). In twelve varieties no virus has been detected whilst 

 in four there is evidence of the presence of viruses differing from any known 

 in this country. Infection of some of the twelve healthy varieties with 

 European viruses has shown that they react to them as do varieties of the 

 domestic potato ; thus two react to X by top necrosis whilst others exhibit 

 leaf-drop-streak with Y. 



Discussion (11.50). 



(concurrently with above session.) 



Miss E. R. Saunders.— r^e neglect of anatomical evidence in the current 

 solutiotis of problems in systematic botany (lo.o). 

 The neglect of anatomical evidence in the analysis of the angiosperm 

 flower has led to the acceptance of many erroneous interpretations. Some 



