. Botany for high schools. Botany. SPECIAL ASPECTS OF NUTRITION OF PLANTS 121 for man would be greatly reduced in price. In former years it was held by some scientific men, that the ordinary green plants could use directly the free nitrogen of the air for food. Careful experiments have demonstrated, however, that this is not the case. Still it has been known for many years that leguminous plants (clover, peas, beans, alfalfa, vetches, honey locust, soja beans, etc.) will grow, thrive, and bear a good crop in soil very poor in nitrogenous plant food provided the other conditions are favorable.
. Botany for high schools. Botany. SPECIAL ASPECTS OF NUTRITION OF PLANTS 121 for man would be greatly reduced in price. In former years it was held by some scientific men, that the ordinary green plants could use directly the free nitrogen of the air for food. Careful experiments have demonstrated, however, that this is not the case. Still it has been known for many years that leguminous plants (clover, peas, beans, alfalfa, vetches, honey locust, soja beans, etc.) will grow, thrive, and bear a good crop in soil very poor in nitrogenous plant food provided the other conditions are favorable. 202. Root tubercle bacteria.—Careful investigations have shown that this is due to the work of microorganisms in the roots of these plants. These bacteria are widely distributed over the earth in nearly all soils, especially in regions where legum- inous plants grow. These bacteria enter at the root hairs, extend by growth in the form of a thread into the cortical region of the root where they stimulate the root cells to the formation of a gall or tubercle, which is often of different form in different species of legumes. These root tubercles are short and thick, often oval in form, or short, cylindrical and branched. They are stouter than the roots to which they are the'common vetch, attached, so that they are easily seen when tubercles, the clover, pea or other legume is dug up and the soil carefully washed from the roots (fig. 90). 203. Within the root tubercle the bacteria spread by means of branched threads or tubes. The cells of the tubercle are rich in protoplasm. Within the cells great numbers of free bacteria are formed which are oval or rod-hke or Y or X shaped. The bacteria in this condition are filled with nitrogenous sub- stances which they have formed by assimilating (or fixing^^) * Certain bacteria, also called microbes. The name now generally used for this particular microorganism is Pseudomonas radicicola. Earlier names are Phytomyxa leguminosarum, Rhizohium
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
