. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. ROOT-NODULES OF leguminosae;. lOI Did they obtain it from combined nitrogen present in the air? To settle this question, peas were grown under bell-jars in washed air, , in air from which all the nitric acid and ammonia had been removed, and the growth was just as good as in the unwashed air. Growth was also good on nitrogen-free soil in a closed space in a limited volume of air which could have offered to the plants only a trace of combined nitrogen (fig. 32). The conclusion, therefore, appeared to be irresistible tha
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. ROOT-NODULES OF leguminosae;. lOI Did they obtain it from combined nitrogen present in the air? To settle this question, peas were grown under bell-jars in washed air, , in air from which all the nitric acid and ammonia had been removed, and the growth was just as good as in the unwashed air. Growth was also good on nitrogen-free soil in a closed space in a limited volume of air which could have offered to the plants only a trace of combined nitrogen (fig. 32). The conclusion, therefore, appeared to be irresistible that the peas were in some way able to assimilate free nitrogen. Boussingault having already shown that legumes can not directly assimilate free nitrogen, the only hypothesis open was some indirect assimilation through the assistance of other organisms. They were led to the conclusion that the root-nodule organism was the factor sought, by having observed that after peas had used up the stored food in the seed there often followed a period of nitrogen-hunger during which growth stopped and the leaves became pale or yellow, but that after a time the green color returned and growth was resumed. In certain plants, however, this resump- tion of vigorous growth never took place and the roots of such plants were observed to be nearly or quite destitute of root-nodules, whereas the roots of the other plants bore nodules, and the more abundant and better developed these were, the better the growth of the plants appeared to Fig, 33.* The next step, therefore, was to add and exclude nodules or nodule products, and so determine the results experimentally. This was done by taking 40 experimental pots containing nitrogen-free soil, holding 30 for checks, and to the other 10 adding 25 cc. of an extract of fertile soil, containing only I mg. of nitrogen per pot, all being planted to peas. All passed through a period of nitrogen- hunger, but the plants in the pots inoculated with the soil-ex
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