Bacteria in their Relation to Vegetable Tissue. 13 



Infection experiments with Galloway's oat-disease succeeded 

 usually with young plants when they were simply sprayed, but older 

 and more developed plants failed to "take" the infection this way. 

 This may possibly indicate that the stomata do not function as a 

 means of entrance, as the older plants are furnished with these 

 structures as well as the young seedlings. 



Kellerman thinks that Bac. sorghi is able to penetrate the roots of 

 the sorghum cane, as the young roots are often attacked during the 

 disease, the infection coming apparently from the soil. Whether 

 they pierce the epidermis itself, or enter by means of the root-hairs, 

 he did not determine. Beyerinck found that through the root-hairs 

 of the Leguminosse, Bacillus radicicola was able to enter and cause 

 the formation of tubercles. 



THE ACTION OF BACTERIA WITHIN THE TISSUES. 



How are bacteria able to spread throughout the tissues of the 

 plant ? We have seen, in the results already detailed, that with certain 

 forms, mainly saprophytic, they are able to pass from cell to cell. 

 That they do this in plant-diseases is evidenced by the lesions that 

 they call forth. But just how they are able to make their way from 

 cell to cell is by no means so evident. In the light of our present 

 knowledge concerning the transpiration stream, we cannot conceive 

 of this current being utilized as a bearer of solid particles unless they 

 have an inherent power of penetrating the cell wall. We do not find 

 that the bacterial plant-diseases are able to spread their infective 

 material throughout the plant in a manner comparable to a septi- 

 caemia, which is often developed in animals. This they would be 

 able to do if the transpiration current could function, like the blood 

 stream, as a distributor of infection. 



It is possible that the lumina of the vascular tissue afford the 

 least resistance to the spread of infection, yet, so far as .we now 

 know, only one parasitic species has adapted itself to this course. 

 Wakker's Bac. hyacinthi affects primarily the xylem tissue of the 

 fibrovascular bundle. Not only does it occupy the cavity of these air 

 cells, but also attacks the surrounding walls, chiefly the middle 

 lamella, which it soon converts into a disorganized gummy exudate, 

 and is thus able to spread to the surrounding tissue. 1 Through these 



1 Wakker: Arch, neer., T. XXIII, p. 6 (1888). 



