46 BACTERIA IN RELATION TO PLANT DISEASES. 



One grower noticed that tomato plants cultivated on soil which had been exposed to the air by- 

 spading were healthy, while those set into the same house in soil left untouched all winter contracted 

 the disease which had been present the previous year. This I/aurent thinks is due to the fact that 

 the bacilli living saprophytically on the roots retained their virulence in the one case, while in the 

 other where the decomposition of the roots was more rapid, the organisms had lost their virulence. 

 The following properties of Bacillus coli as a parasite on potato are given : It did not develop 

 at io° to 12° nor above 40°. It did not attack the cellulose of filter paper, or that of cotton, the 

 pith of elder, or the seeds of the date palm, even if glycerin was added to the culture to permit 

 rapid development of the organism. Liquids obtained by diluting and then filtering the pulp of 

 attacked tubers, even those very active on the tissues of potatoes, resulted in nothing, even after 

 several days, when tried on the varieties of precipitated cellulose. Cultures in peptonized bouillon, 

 heated for 5 minutes at 75° are sterilized. The bacillus did not show any spores. 



The surfaces of his tubers were not sterilized before cutting, they were only washed and 

 then cut with a flamed knife. No checks appear to have been kept, i. e., each half was 

 inoculated. If I did things in this way I should expect to have mixed cultures continuously. 

 Possibly all these results were obtained with Bacillus coli, but of this I am somewhat scepti- 

 cal. The inoculated things were kept generally in covered crystalizing dishes, or under 

 bell-jars, containing sterilized water. 



Jensen (1900) experimented along the same lines as Laurent but could not get the same results. 

 He concluded, therefore, so far as he could draw conclusions from his experiments, that the true 

 Bacillus coli is not able to attack raw potato tubers which have been made alkaline with NaOH. 

 When B. coli made any growth at all it was confined to the thin surface layer which had been killed 

 by the alkali. The living cells beneath had normally acid cell-sap. On most of the potatoes no 

 growth was visible. He used i per cent and 2 per cent solutions of NaOH and the tubers were first 

 thoroughly scrubbed and soaked for 2 hours in 2 per cent corrosive-sublimate water and then cut 

 with a sterile knife and handled with sterile forceps. The results were quite otherwise when less 

 care was taken to work under sterile conditions, e. g., when the potatoes were cut with an unsteril- 

 ized knife. Then after some days the surface was covered with an abundant bacterial flora, but 

 pieces inoculated abundantly with B. coli bore no more bacteria than uninoculated pieces. In some 

 cases these intruders attacked the sound parts of the potato with solution of the intercellular sub- 

 stance and gas formation, but in most cases only the part killed by the NaOH was attacked, 

 it mattered not whether the tubers were inoculated with B. coli or were uninoculated. 



In 1902, Lepoutre published a paper on the experimental transformation of saprophytic bacteria 

 into plant parasites. The question before him was whether this transformation could be induced 

 in other bacteria than those Laurent had experimented with. 



He states that his experiments were carried on with three species, B. fluorescens liquefaciens, 

 B. mycoides, and B. mesentericus vulgatus, but one can not be at all certain from anything in his paper 

 that he really had these particular species under observation. His field for experiment was the same 

 that Laurent used and was divided into five plots. Each year plot I received an excessive appli- 

 cation of nitrogenous fertilizer; plot II, of potassium; plot III, of superphosphates; plot IV, of 

 lime; and plot V of sodium chloride. 



The bacteria studied were sowed on the surface of sections of potato or carrot placed in closed 

 crystallizing dishes and kept in the thermostat at 30°. 



The first attempt was made with an organism found in a decaying potato, and which, in con- 

 sequence had some initial virulence. His identification of it as B. fluorescens appears to have been 

 a rather offhand one, to wit: "Une culture sur bouillon gelatine m'assura que c'etait bien cette 

 espece. " A little of the infected pulp was placed on slices of carrot. On the third day some blackish 

 glairy spots appeared on the sections of roots from plots I and V. The others were unaffected. 

 The sections were then trimmed (refraichies) and reinoculated, this time with the product of the 

 previous inoculation on sections from plot I. After 2 days development had taken place only on sec- 

 tions from plots I and V, but the attack on the tissues was more pronounced than in the former 

 passage, especially on the roots from plot I. 



Turnips from the five plots were then inoculated with B. fluorescens obtained from the last 

 passage upon carrots from plot I, and with B. mycoides and B. mesentericus vulgatus from bouillon 

 cultures. The first of these showed itself the most active of the three. Roots from plot I were most 

 predisposed to infection. These were attacked to a depth of 5 mm. The parenchyma was com- 

 pletely disintegrated and replaced by a very soft, decidedly alkaline pulp. The other two species 

 caused only a slight attack on turnips 3 days after inoculation, the most being on turnips from 

 plots I and IV. 



