\2 BACTERIA IN RELATION TO PLANT DISEASES. 



beer. The mould did not develop, but on a slice of carrot from plot IV, there appeared a little 

 bacterial colony of a ropy consistency, made up of short bacilli, introduced probably when the conidia 

 were sowed. All his attention was then focussed on this bacillus. 



Inoculations were made with a flamed scalpel on slices of carrot kept at laboratory tempera- 

 ture. Sections from plots II and IV became infected in 4 days while those from I and III remained 

 uninjured. Two later attempts to inoculate I and III failed. 



Inoculations of slices of carrots from all plots, using the microbe obtained from IV of the preced- 

 ing series, gave positive results. Another series using material from plot II of the second series 

 gave a general development on roots from plots I, II and IV, but scarcely any colonies on those 

 from III. 



A fourth series, however, inoculated with bacteria taken from slices of plot I (third series, kept 

 at a temperature of 25 C.) gave a growth on all the slices from all the plots. 



Thus the microbe had become parasitic even upon the most resistant carrots after three pas- 

 sages through less resistant ones. 



Results absolutely comparable were obtained with tubers of potatoes: Thus, tubers from plot 



IV were readily attacked, those from plots I and III less so, while those from plot II were success- 

 fully inoculated only after four passages of the bacillus through tubers from plot IV. 



When the microbe grew it finally transformed the invaded tissues into a pulp, composed of 

 disassociated cells in which the starch-grains persisted. The cylindrical bacilli swarmed around 

 and finally within the cells. 



This schizomycete was identified as B. fluorescens putidus. It was readily cultivated in a 

 mineral solution: 



Water 1,000. 



Neutral ammonium phosphate 2.5 



Neutral potassium phosphate 2.5 



Magnesium sulphate 1.0 



to which had been added various organic matters sugars; alcohols; peptone; asparagin; succinate, 

 lactate, citrate and tartrate of potassium, etc. but in such cultures it lost its virulence, to such an 

 extent that inoculations on tubers from plot IV gave negative results. Only by diminishing the 

 resistance of the potato cells by the use of alkaline solutions was infection made possible. 



In March, a new series of experiments was begun, the four plots receiving fertilizers per hectare 

 as follows : 



Plot I. 500 kg. sodium nitrate and 800 kg. sulphate of ammonia. 



Plot II. 2,000 kg. kainite, containing 13 per cent of potash. 



Plot III. 2,000 kg. superphosphate of lime, containing 15 per cent of phosphoric acid. 



Plot IV. 40.000 kg. quick lime. 



A fifth plot received 2,750 kg. sodium chloride per hectare. This was to determine what effects 

 might be attributed to the osmotic action of large quantities of soluble salts. In a sixth plot the 

 plants mentioned below were cultivated without special fertilizers: Eight varieties of potatoes 

 were used, namely three which had the reputation of being subject to disease, viz., Marjolin, Early 

 Rose, and Blanchard; three considered to be resistant, viz., Chave, Simson and Chardon; and two 

 other sorts, viz., Pousse Debout and Zeland. The tubers of Simson used as seed were harvested 

 from the corresponding plots of the previous year. In addition to potatoes, Nantes carrot, Witloof 

 chicory, Jerusalem artichoke and a local variety of sugar beet were cultivated on these plots. 

 All the seed-tubers sprouted and developed regularly, but in plot V the salt plainly injured the 

 germination of seeds. 



At the time for inoculation, the fluorescent bacillus was found to be lacking in virulence as it 

 had been kept on artificial media. Therefore, Laurent undertook to get the bacillus as in the 

 first place, but obtained this time a motile nonfluorescent organism (2 to 5 x 0.5 to 0.6 ,u) the 

 colonies of which it is said resembled those of Bacillus coli. Submerged colonies were little yellowish 

 disks, while surface ones were pearly white, spreading, with a circular or sinuous border. 



The different varieties of potatoes yielded very differently in the several plots, showing that 

 each variety has its own requirements as regards mineral foods. 



Halves of tubers of Marjolin from all the plots were inoculated with the bacillus from tubers 

 of plot IV, and kept in the thermostat at 30. All were attacked within 6 hours, but while penetra- 

 tion continued in sections from plot IV, reaching 10 to 12 mm. by the fourth day, it ceased in all 

 the others by the second day, with a healing of the spots. 



Slices of Early Rose from all plots, inoculated with cultures from tubers of plot IV in the pre- 

 ceding experiment and kept at 30 , offered little resistance to the disease, except in tubers from plot 



V where the sticky surface layer reached a thickness of 4 to 5 mm. 



