98 



Mycologia 



The following review of Mr. M. C. Potter's paper, " Uber eine 

 Methode, parasitare Krankheiten bei Pflanzen zu bekampfen " 

 (Centralb. f. Bakt. 2 ser. 23: 379-384. 1909), has been kindly 

 contributed by Mr. E. D, Clark : 



Pseudomonas destructans is the cause of the so-called "white 

 rot " of the beet. This parasite secretes an enzyme, cytase, which 

 dissolves the cell-walls of the plant, allowing the toxin of the 

 parasite to come into direct contact with the protoplasm of the 

 host, which is thus quickly destroyed. Both the cytase and toxin 

 of P. destructans are very powerful, making the organism very 

 virulent. In many cases the products of the life activities are 

 toxic to the growth of a given plant or animal if not removed. 

 This is true in the case of the present organism, for the author 

 found that it produces substances toxic to its further growth, 

 whatever it grows upon. The author's experiments indicate that 

 the toxin thus produced by the growth of the parasite is able to 

 withstand boiling, while the cytase, like most enzymes, is com- 

 pletely destroyed by such treatment. Some of the solutions 

 containing the toxin and cytase were concentrated by vacuum 

 distillation at 60°, which did not alter the toxin, but destroyed 

 the activity of the cytase. In all concentrations, including that 

 of the original culture liquid, the toxin solutions completely 

 stopped further growth of P. destructans, both on the beet and 

 in other nutrient media, and, also, as seen under the microscope, 

 all movement was immediately inhibited. The toxin solution is 

 specific in its action only on the parasite producing it, but it also 

 shows a certain destructive effect on the host cells, although the 

 latter soon heal over, since no cytase is present to destroy the 

 cell-walls. Next, the author prepared in the same manner toxin 

 solutions from Penicillium italicum, which is the cause of a 

 destructive disease of oranges, lemons, etc. Ths solution showed 

 exactly the same specific inhibiting qualities shown by that of 

 P. destructans. From these observations, the author thinks it 

 possible that such toxin solutions obtained in a similar way from 

 growths of bacteria, fungi, etc., might prove to be of great 

 practical importance in combating the ravages of these organisms. 



