14 H. L. Russell. 



elongated vessels it is able to spread the disease quite rapidly, as 

 has been demonstrated by artificial infection experiments. 



The rapidity with which the pear-blight germ is able to spread its 

 infective material through a susceptible host also indicates a very 

 rapid movement from cell to cell. This is especially marked in the 

 softer succulent tissue of the youngest twigs and in the blossoms. 

 After once securing an entrance to the rapidly growing tissues, it 

 sets up a kind of fermentation which completely destroys many of 

 the cells, thus forming large spaces which are filled with the gummy 

 products of its fermentative activity. Under favorable conditions, 

 the rapidity with which the blight bacteria spread is quite surprising. 

 The following laboratory note may be considered fairly indicative of 

 the rate of distribution. March 8, a Japan seedling was infected by 

 puncture of the young stem. March 13, the disease had manifested 

 itself by a local blackening of the tissue in the neighborhood of the 

 inoculation point. Two days later, the stem showed that the 

 disease had progressed fully six inches from point of inoculation, as 

 indicated by blackened appearance. The presence of bacteria was 

 also demonstrated microscopically fully an inch or more beyond 

 this blackened tissue, showing that the spread of the disease, after 

 having once established itself, was quite rapid. 



It has been suggested that bacteria are able to pass from cell to 

 cell through minute pores in the walls. Recent investigations 1 show 

 that the direct union of the plasma of cell to cell is very much more 

 widely diffused than was formerly supposed, and that all the living 

 elements of the whole plant-structure of higher plants are thus united. 



These plasmic strand-connections vary in diameter from 0.05-1.0^, 

 but on the average they are so small that it would seem hardly 

 possible that they coul^ be utilized by the bacteria in forcing their 

 way from cell to cell. It seems much more probable that their 

 progress is effected by ferment activity. In the case of the pear- 

 blight germ and the hyacinth-disease, it is seen that the healthy 

 tissue undergoes a decomposition under the influence of the bac- 

 teria, resulting in the production of a gummy substance, and in the 

 case of the blight, the liberation of CO 2 . 



Bolley 2 finds the germ causing the surface scab in the potato im- 



1 Kienitz-Gerlofi : Bot. Zeit. (1890), XLIX, 1. 



2 Bolley : Agric. Science, IV, 284. 



