RiiSUARCH ON Plant Ti'mors 517 



Modes of overwintering by disease-producing organisms and 

 their transmission by living carriers iiad for many years been 

 investigated in animal and plant pathology. These studies almost 

 invariably had practical bearings, since by eradicating the over- 

 wintering agency and by exterminating the insect carrier effective 

 weapons against the malady's spread were provided. For example, 

 S. P. Doolittle's discovery that wild cucurbits harbor the virus of 

 cucumber mosaic and that the striped beetle transmits the mosaic 

 virus enabled workers to attack this virus disease in part by 

 destroying wild cucurbit vines and by exterminating as far as 

 possible the beetle transmitter.'""' 



Smith, in his address " Fifty Years of Pathology," '°'"' after 

 devoting considerable attention to carriers of human and animal 

 diseases (to be quoted in Chapter XI), expressed his belief that 

 there 



are also many carriers of plant parasites, as many as of animal diseases, 

 and as in animals there are some very striking adaptations, for example, 

 the relation of the striped beetle, Diabrotica vittata, to the bacterial wilt 

 of cucurbits, worked out in detail by F. V. Rand in my laboratory. Here 

 all the beetles, apparently, transmit the disease in the summer, but only 

 a small proportion of those that have wintered over are able to do so, 

 that is, those only whose intestinal juices have not been able to destroy 

 the ini^ested microbes. From the feces of these individuals come the first 

 spring infections. In other words, these particular beetles behave exactly 

 like human typhoid carriers. Rand lists nearly 50 plant diseases known or 

 suspected to be transmitted by insects. 



In 1920 Rand and W. Dwight Pierce published in Phyto- 

 pathology ^°' a study entitled "A Coordination of Our Knowledge 

 of Insect Transmission in Plant and Animal Diseases." 



In his letter to Moore, Smith told also that " recently Dr. Harry 

 Braun of this laboratory has devised a new seed treatment wdiich 

 bids fair to be of great importance in controlling various seed- 

 borne diseases." In his Introduction to Bacterial Diseases of 

 Plants,^°^ he had said that by Braun's discovery "(1919) . . . 

 injury to seed-wheat, which is considerable when formalin solu- 

 tions or copper sulphate solutions are used, is eliminated by 



^°^ Fifty years of pathology, op. cit., 37. At p. 36 Smith also mentioned I. C. 

 Jagger's transmission of cucumber mosaic diseases by rubbing crushed leaves of 

 diseased plants on healthy plants (1917). 



"■"^Op. cit., 42. '" 10(4): 189-231, Apr. 1920. "« Pp. 71-73. 



