A Bacterial Disease of Stone Fruits 



415 



The organism gains entrance to the host through the stomata (Figs. 68 

 and 69) and the young lenticels during periods of sufficient moisture. A 

 film of water on the sur- 

 face of the leaf, the twig, 

 or the fruit enables the 

 bacteria to move about 

 and gain entrance to 

 the substomatal cavity. 

 Inoculation ordinarily 

 does not take place in 

 the absence of moisture. 

 Lenticels and stomata 

 are fairly well distrib- 

 uted on the young twigs, 

 and the stomata are 

 more or less plentiful 

 on the green fruit and 

 on the lower surface of 

 the leaves, but there 

 are none on the upper 

 leaf surface. Consequently inoculation may occur anywhere on the 

 young, tender twigs and the green fruit, while on the leaves the 

 organism can gain entrance only from the lower side. 



In 1911, at Ithaca, New York, 332 Elberta peach leaves of different 

 ages were inoculated in the early morning. A few drops of water 

 containing numerous bacteria in suspension were placed, by means 

 of a pipette dropper, on the upper or the lower surface of each 

 leaf. In all, 149 of the leaves were inoculated on the upper, and 

 183 on the lower, surface. In four weeks 177 of the leaves inocu- 

 lated on the lower surface contained many spots; 6 were clean. 

 All the 149 leaves inoculated on the upper surface were free from 

 infection. In the same year 100 plum leaves were inoculated in 

 the same way, 40 on the upper and 60 on the lower surface. At the 

 end of five weeks, 55 of the leaves inoculated on the lower surface 

 contained many brown spots, and 5 were free from lesions. All the leaves 

 inoculated on the upper surface were free from spots. All the check 

 leaves were normal. 



Fig. 69.— Early stage of fruit spot on Burbank plum 

 fruit. The fruit had been inoculated with a strain of 

 Bacterium Pruni, isolated from a peach tree. The 

 material was collected seven days after the inoculation 

 ivas made. It was fixed in strong alcohol, infiltrated 

 with paraffin, and cut on the microtome. The sections 

 were stained with acid fuchsin. (Drawing outlined 

 with the aid of a camera lucida) 



