7A PRESIDENTIAL ADDRESS SECTION C. 



B. malzaccaritm was repeatedly isolated from the film of water 

 coverinoc infected leaves after rain or heavy dew ; and he was 

 able to show experimentally that water is splashed by a falling 

 drop, only when it falls on a film of water, and that it is the water 

 of the film which forms the splash drops. The distance of the 

 splash varies according to the size of the drop, depth of surface 

 films, elevation and inclination of the surface of impact, and the 

 velocity of the wind. A drop of .02 c.c. in volume, falling 

 16 feet upon a relatively thin film of water, and a plate 3 feet 

 above the ground, during a wind of 10 miles an hour, splashed 

 v;ater in abundance a distance of 8 feet in moderate quantities as 

 far as 12 feet, and in slight amounts to 16 feet. The possibilities 

 of dissemination of the motile bacteria, which have been shown 

 to emanate from lesions into the surface water film, during a 

 driving rain, are therefore considerable, if one includes the 

 distance bacteria may be carried from the original lesion, then 

 splashed up and carried farther, and so on, imtil a dilution too 

 great for infection is obtained. 



Rain-si)lash infection is probably responsible for a large 

 proportion of stomatal and water pore infection ; but in the case 

 of organisms which enter the host through the nectaries or 

 through wounds, insects are often the agent of transmission. 



The first exact experiments in this connection were carried 

 out by Waite in 1891 (62). He isolated the pear blight 

 organism, grew it in pure culture, and established its patho- 

 genicity l)y inoculations. With these cultures he sprayed blossom 

 clusters in places where the disease did not occur, and obtained 

 blossom blight ; the infection travelled back into the support'ing 

 branch, and later he found the organism multiplying in the 

 nectar, and re-isolated it. On certain trees he protected some 

 of the flowers from the visits of bees by covering them with 

 mosquito netting, and the protected blossoms remained free from 

 disease ; on other trees, where the flowers were not covered, he 

 saw bees visit them, sip from the inoculated blossoms, and then 

 visit blossoms on unsprayd parts of the tree, which soon became 

 blighted. As a final proof he captured bees which had been 

 seen visiting infected blossoms, excised their mouth parts, and 

 from these obtained a culture of Bacillus amyloz'oru.i, with which 

 he again produced the disease. 



Similar experiments, carried out in later years, showed that 

 bees are also resnonsible for conveving a bacterial disease of 

 ■pear blossoms in England (s a) and in South Africa (18) : each 

 of the two latter diseases, however, appears to be caused by an 

 organism distinct from B. ainylovonis, and of a less virulent 

 tvpc. 



Recent! v Stewart ( sS-rio) has shown that various sucking 

 insects, particularly the tarnished plant bug (Lygus pratcnsis) 

 are capable of carrving (B. ■amxlo-rorits) from diseased to 

 healthy shoots, where the bacteria gain entrance to the plant 

 tissues through the feeding punctures made by the insects ; 



