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Effects of Variation in Day-Length and Clipping of Plants on Nodule Development and Growth of Soy Bean

Scott V. Eaton
Botanical Gazette
Vol. 91, No. 2 (Apr., 1931), pp. 113-143
Stable URL: http://www.jstor.org/stable/2471329
Page Count: 31
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Effects of Variation in Day-Length and Clipping of Plants on Nodule Development and Growth of Soy Bean
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Abstract

1. The effects on growth and nodule development of the soy bean of varying certain factors that affect the amount of carbohydrate manufactured by the plants in the process of photosynthesis were studied. The factors varied were length of the exposure to light and the amount of photosynthetic tissue present, differences in the latter being secured by clipping the plants with different degrees of severity. 2. The amount of growth and nodule development was in direct proportion to the length of day and the degree of severity of the clipping. 3. Nodule development was correlated with percentage of carbohydrates, especially acid-hydrolyzable material, of the plants. This correlation was much greater for the tops than for the roots. It is suggested that part of the decrease in nodule development resulting from decrease in photosynthesis is due to a lack of carbohydrates for the nitrogen fixation process. 4. No correlation was noted between the carbohydrate-nitrogen relationship of the plant and growth and nodule development in regard to the effect of this relationship on the development of the roots in proportion to the tops. The roots relative to the tops were better developed in the shorter than in the longer exposures. This lack of correlation may have been due to the fact that there was not sufficient fractionation of the carbohydrates and nitrogen. 5. Growth and nodule development of the plant were more closely correlated with the amounts of the chemical constituents when figured on an absolute basis than on a percentage basis. It is suggested that, with a decrease in photosynthesis there may be less growth of all parts of the plants, including the nodules, because of the smaller amount of food material present; but that the percentage composition of the resulting plants may be similar, or at least not different enough to account for the difference in the size of the plants. According to this viewpoint, the amounts of the chemical constituents figured on an absolute rather than a percentage basis may be more important in explaining the effects of the treatments. 6. The degree of greenness of the plants was in direct proportion to the length of exposure to light, and the phenomenon of etiolation was very prominent in the case of plants of the shorter exposures. 7. The plants resulting from a variation in day-length in the spring and from clipping were similar in type in regard to time of bud development, absence of twining, etc. The plants exposed to different day-lengths in the autumn were very different in type, the long-day plants being relatively vegetative, with a better development of tops in proportion to the roots, non-fruitful, and twining; the short-day plants being relatively non-vegetative, with a poorer development of tops in proportion to the roots, fruitful, and non-twining. However, nodule development of the autumn-grown plants was similar to that of the spring-grown, varying directly with the length of exposure to light. 8. Various external factors which might account for the fact that the plants exposed to different day-lengths were similar in the spring but different in the autumn are day-length, intensity of light, quality of light. Differences in the quality of the light may be an important factor. 9. Whatever were the external factors accounting for the differences in the types of plants when day-length was varied in the autumn, the carbohydrate-nitrogen relationship did not explain the differences. This may have been due to the fact that there was not sufficient fractionation of the carbohydrates and nitrogen.

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