. Les bactéries dans le cadre de maladies des plantes. Bactériologie ; maladies des plantes. 98 bactéries PAR RAPPORT AUX MALADIES DES PLANTES. La croissance a toutefois été obtenus dans certains cas, il semblerait, sur des sols pratiquement dépourvus d'azote combiné, et aussi, je crois, dans un climat dépourvu de toute trace d'azote combiné, ;. c, d'ammoniac et d'acide nitrique. La figure 32 montre un pois cultivés jusqu'à maturité dans un espace fermé sur le sable sans azote (sur lequel l'avoine et le sarrasin affamé) en ajoutant de l'extrait de sol contenant de l'azote- racine organisme des nodules. Cet extrait de l'eau ne contient que 0,15 mg de l'azote, un

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. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. 98 BACTERIA IN RELATION TO PLANT DISEASES. growth has, however, been obtained in some instances, it would seem, on soils practically destitute of combined nitrogen, and also, I believe, in an atmosphere destitute of all traces of combined nitrogen, ;. c, of ammonia and nitric acid. Figure 32 shows a pea grown to maturity in a closed space on nitrogen-free sand (on which oats and buckwheat starved) by adding soil extract containing the nitrogen root- nodule organism. This water extract contained only 0.15 mg. of nitrogen, and the hermeti- cally sealed carboy was opened to the date of the photograph (fiftieth day) but three times and then for a few moments only to introduce a measured quantity of pure washed carbon dioxide (6 liters) necessary for the growth of the plants. The capacity of the carboy was 44 liters and while the contents of the air in combined nitrogen was not deter- mined it could not have been over a small fraction of a milligram. The pea grew for a period of 4 months and fruited, yielding a total dry weight of 10.359 grams, of which 233.5 nigs, were nitrogen. Some nitrogen was also re- covered from the sand, making (after proper deductions for nitrogen in the seeds, etc.) 248 mgs. of fixed nitrogen. The oats and buckwheat made only a very starved growth and finally perished without fruiting. It will be remembered that Boussin- gault got no growth and no nitrogen assimilation in a closed space under sterile conditions. This is exactly Boussingault's experiment plus the addi- tion of soil extract containing root- nodule bacteria, the result being entirely different. The bacteriologist finds that in pure cultures the root-nodule organism appears to be able to grow on substrata in which there is absence of nitrogen compounds or at least great paucity of such compounds. Maze states that the organism requires a minimum of com- bined nitrogen to make a good growth and store nitrogen. He

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