. Nature and development of plants. Botany. NATURE OF PLANTS 65 in their growth. If this plant happens to contain foods suitable to the dodder then a second stimulus is aroused which causes root- Hke branches to form. These organs penetrate the branches upon which the dodder is growing and absorb foods from it. Many plants live as parasites on the roots of a variety of herbaceous and woody plants, as the beech drop, orobanches, broom rape, Fig. 38. Tubercles formed on roots of lupine by nitrogen fixing bacteria. One of the most remarkable features of roots and one of the most important i
. Nature and development of plants. Botany. NATURE OF PLANTS 65 in their growth. If this plant happens to contain foods suitable to the dodder then a second stimulus is aroused which causes root- Hke branches to form. These organs penetrate the branches upon which the dodder is growing and absorb foods from it. Many plants live as parasites on the roots of a variety of herbaceous and woody plants, as the beech drop, orobanches, broom rape, Fig. 38. Tubercles formed on roots of lupine by nitrogen fixing bacteria. One of the most remarkable features of roots and one of the most important in the economy of the earth is seen in that large family of bean or leguminous plants that are characterized by flowers and fruit like those of the pea. Minute plants, bacteria, gain access to the roots of these plants through the root hairs and cause wart-like enlargements, tubercles, on the roots (Fig. 38). These bacteria have the power of combining the nitrogen of the air with other elements, termed the fixation of nitrogen, and so forming a nitrogen-bearing compound that can be ab- sorbed by the plant. To give an idea of the importance and work of these bacteria, it is estimated that an acre of clover yielding two tons contains 100 lbs. of nitrogen—74 lbs. of which has been derived from the air. The fixation of this amount of nitrogen by the bacteria in the roots of the clover would nearly suffice for the production of 50 bushels of corn and 30 bushels of wheat. Nitrogen is one of the very essential elements re- 5. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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