[Vol. 2 



388 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



terium Solanacearum). The pear blight organism probably 

 dies out of soils quickly as it does in a majority of the blighted 

 branches. Pear blight by soil infection is not known. 



Among extraneous agents, wind and water have been sus- 

 pected. I have never seen any clear indications of wind-borne 

 infection, not even when conditions seemed to invite it, but 

 water often carries parasites and furnishes conditions favor- 

 able to infection. Home has shown that the olive tubercle in 

 California is transmitted in this way. Honing, in the tobacco 

 fields of Sumatra, has traced infection several times to the 

 watering of plants from infected wells, and has cultivated 

 the parasite from the water. I have discovered experi- 

 mentally that to obtain several sorts of bacterial leaf-spots 

 (bean, cotton, peach, plum, carnation, larkspur, sorghum, 

 geranium) the surface of the leaves must be kept moist to the 

 same extent they would be in case of prolonged dews or fre- 

 quent light showers. Such conditions are necessary to enable 

 the bacteria to penetrate the stomata and begin to grow. In 

 case of water-pores, however, the plant itself furnishes the 

 water necessary for infection, if the nights are cool enough, 

 i. e., if the air remains near enough to saturation to prevent 

 for some hours the evaporation of the excreted water from the 

 leaf-serratures. Every plant with functioning water-pores 

 awaits its appropriate bacterial parasite. The genus Im- 

 patiens is a good example. I have looked on it for one in 

 vain but I am sure it must occur. 



Man and the domestic animals, especially through the 

 agency of the dung-heap, infallible repository of all sorts of 

 discarded refuse, undoubtedly help to spread certain bacterial 

 diseases of plants (potato rots, black rot of cabbage, etc.). 



Birds probably transmit some of these diseases on their 

 feet or in other ways. In connection with the bud-rot of the 

 coconut palm in the West Indies, I suspect the turkey-buzzard, 



but the evidence 



Mr. Waite ob 



tained (once in Florida, once in Maryland) the strongest kind 

 of circumstantial evidence going to show that pear blight may 

 be spread by birds. 



