48 BACTERIA IN RELATION TO PLANT DISEASES. 



separated into three parts. To one part (A) was added 2 per cent oxalic acid, to the second (B) a 

 little lime water, and the third part (C) was heated to 62 C. for 5 minutes. A drop of essence of 

 mustard was added to prevent invasion by bacteria. Small slices of carrot, turnip, and potato were 

 plunged into these liquids. Two hours afterward the superficial tissues in A and B were disorgan- 

 ized and the protoplasm in the cells contracted. In C the tissues remained compact but the pro- 

 toplasm was more decidedly contracted than in B. 



Here are found the two agents described by Laurent, an enzyme which dissolves the middle 

 lamellae, and a substance which contracts the protoplasm. The former is destroyed at 62C, and 

 works best with B. fluorescens on acid media; the latter is resistant to a temperature of 62 . 



Similar experiments were made with the juice from infected potatoes with similar results. 

 An enzyme was present which dissolved the middle lamellae in the presence of lactic and acetic acid 

 accompanied by coagulation of the protoplasm. An alcoholic precipitate from the filtered extract 

 of these cultures when dissolved in water caused disintegration of the membranes. The presence 

 of acetic and lactic acids in the same liquid was revealed by analysis. 



The protoplasm of potatoes is not contracted by a 1 per cent solution of these acids, though that 

 of Jerusalem artichokes, carrots, and onions is thus affected. Such a concentration is probably not 

 reached in cells at the limit of the contaminated tissues. Other products of secretion add their 

 toxic action to those of the acids and determine the death of the cells before the penetration of the 

 bacteria. Cellular separation due to the action of an enzyme must take place before the bacteria 

 can penetrate the tissues. This enzyme appears to diffuse more slowly than the toxic substances. 

 Alkalinity in the pulp containing bacteria is due to the products of the decomposition of nitrogenous 

 materials contained in the cells. Thus ammonia is formed, which neutralizes the acids. Its presence 

 is evident from the odor, and it may be liberated by distillation with potash. 



The intervention of ammonia is necessary to prevent the toxic action of organic acids pro- 

 duced by the bacteria in the decomposition of sugars. Thus, he thinks, may be explained the pre- 

 disposition of tubers from plot I, where nitrogenous fertilizer was used. 



A nitrogenous alimentation provokes a more important assimilation of nitrogenous compounds, 

 albuminoid substances, amides, or others, all very favorable to the nutrition of bacteria and to the 

 production of residual ammoniacal compounds. 



Recently M. Peterman has called attention to the great amount of non-albuminous nitrogenous 

 material in tubers of potatoes subject to Peronospora, and a corresponding lack in resistant varie- 

 ties. This is new evidence for the relations existing between the composition of plants, their 

 alimentation, and the development of their parasites. This relation should be as true for mineral 

 substances as for organic ones; for carbohydrates as for nitrogenous compounds. 



The following is given as an example: Cultures of B. fluorescens made in April on potatoes 

 were unsuccessful. The potatoes were immune. The same was true in May on diverse varieties. 

 The organism seemed to have lost its virulence. In June, however, similar cultures on new potatoes 

 gave positive results; the bacteria were again active, and several passages on potato restored their 

 former virulence completely. This immunity in spring may be explained only by the exhaustion 

 of reserve sugars by respiration and by the growth of shoots. B. fluorescens, incapable of attacking 

 starch, is not able to produce from the old tubers the toxic substances which kill the parenchyma 

 of the tuber. Here immunity results from impoverishment of the host. 



At the suggestion, and under the guidance of Beyerinck, Dr. van Hall undertook a 

 series of experiments to determine which of the saprophytic bacteria in the soil are able to 

 cause decay in the subterranean part of plants, i.e., are facultative parasites. In 1902, as a 

 result, he published a paper on Bacillus subtilis and Bacillus vulgatus as plant parasites. 

 The following is an abstract of this paper : 



He placed in Petri dishes, on moist filter paper, freshly cut slices of different plants. Over some 

 he poured a small amount of water in which soil had been shaken; others he streaked with damp 

 soil. The soil used was taken from several localities. Decay did not occur in any case at room 

 temperatures (23 , 30 C), but was obtained very often at thermostat temperatures (37 , 42 C). 

 In every case, with one exception, decay was caused by one or other of two bacilli, identified as above. 

 No others appeared when, according to Laurent's method, the slices were kept for an hour in 1 per 

 cent solution of potassium hydroxide before inoculation, to reduce the acidity of the cell-sap. 



Bacillus subtilis attacked Jerusalem artichokes, potatoes, and hazel nuts. After 24 hours in 

 the thermostat at 37 C, slices of the artichoke and potato inoculated as above showed moist dark- 

 colored spots on an otherwise dry white surface. These spots spread rapidly and after another 24 

 hours covered almost the entire surface. These spots swarmed with bacteria all, or almost all, of 

 which belonged to B. subtilis as shown by colony cultures. The spots on the hazel nut were slimy 

 but uncolored. 



