1915] 



SMITH BACTERIAL DISEASES OF PLANTS 



389 



molluscs, and worms, the evidence is 



I have 



Respecting insects, 



mplete. They often serve to carry these diseases 



summarized our knowledge in another pi 



and will here 



by insects long before the animal 



content myself with a brief statement calling renewed atten- 

 tion to the subject. 

 We had very good evidence of the transmission of one bac 



terial disease of plants 

 pathologists awoke to the importance of the subject, 2 but it 

 cannot be said that they have ever paid much attention to it, 

 although it antedates by two years the work by Theobald 

 Smith and Kilborne showing that Texas fever is transmitted 

 by the cattle tick (Ixodes bovis). That discovery also belongs 

 to the credit of the U. S. Department of Agriculture, and the 

 two together may be said to have laid broad and deep the foun- 

 dations of this most important branch of modern pathology. 

 Waite isolated the pear blight organism, grew it in pure cul- 

 tures, and proved its infectious nature by inoculations. With 

 such proved cultures he sprayed clusters of pear flowers in 

 places where the disease did not occur and obtained blossom- 

 blight, and later saw this give rise to the blight of the sup- 

 porting branch, found the organism multiplying 



and reisolated it from the blighting blossoms 



On some tr 



he restricted the disease to the sprayed flowers by covering 

 them with mosquito netting to keep away bees and other 

 nectar-sipping insects. On other trees where the flowers were 

 not covered he saw bees visit them, sip from the inoculated 

 blossoms and afterwards visit blossoms on unsprayed parts of 

 the tree which then blighted. Finally he captured bees that 

 had visited such infected blossoms, excised their mouth parts, 

 and from these, on agar-poured plates, obtained Bacillus 

 amulovorus, with colonies of which he again produced the dis- 



These experiments were done in several widely sepa- 

 rated localities with identical results. I saw them and they 

 made a great impression on me 



1 Smith, E. F. Bacteria in relation to plant diseases, 

 ington, Publ. 27": p. 40. 1911. 



ease. 



Wash 



2 Waite, M. B. Results from recent investigations in pear blight. Bot. Gaz. 



40 



1891. 



. 



