1902.] 



Pseudomonas destructans {Potter). 



395 



turnip were quite rotten, but the cuticle remained intact, and could be 

 readily separated as a fine membrane. The experiment was also tried 

 upon leaves and young shoots ; in this case I employed no sterilising 

 agent, which would have been liable to kill the very young epidermal 

 cells. A small portion of turnip about the size of a pin's head, 

 rotten through the action of P. destructans, was placed on the unin- 

 jured surface of a number of mature leaves, and also upon very 

 young ones exposed by removing the outer leaves at the growing 

 points, both sets being kept damp at the temperature of 30° C. After 

 5 days no sign of decay could be detected upon the mature leaves, 



Fia. 2. — Stages in the perforation of the cell-wall by Pseudomonas destructans. 

 At A and B the bacterium is seen passing into the cell from an intercellular 

 space. (Paraffin sections ; 1/12 oil immersion. Compensating oc. 8.) 



but in the young ones the result was very different. These being 

 in a growing condition, and possessing little or no cuticle, offered 

 but a feeble resistance, and after the interval of 5 days had become 

 quite rotten. 



The old and fully developed cuticle is apparently proof against the 

 action of the enzymes excreted by P. destructans, but this parasite can 

 readily effect an entrance into its host through the undeveloped 

 epidermis of young and tender structures. 



This bacterium is incapable of manipulating the hard and tough 

 rind of the sound turnip, but when brought in contact with a wounded 

 surface it at once flourishes as a saprophyte upon the remains of the 

 injured cells; very soon the number of individual bacteria becomes 



vol. lxx. 2 E 



