. Auxins and plant growth. Auxin; Plant growth promoting substances. Occurrence and Role of Growth Hormones 73 tomato (Kramer and Went, 1949). Small, young apices yielded little diffusible auxin and older apices yielded proportionally more, as shown in figure 33. The diffusible auxin more than doubled with each ten day period in the development of the plant. Light is an important factor in auxin formation, although not a simple one. There is some confusion concerning the necessity of light for auxin formation, but in general it would appear that green plants do require light for this function,
. Auxins and plant growth. Auxin; Plant growth promoting substances. Occurrence and Role of Growth Hormones 73 tomato (Kramer and Went, 1949). Small, young apices yielded little diffusible auxin and older apices yielded proportionally more, as shown in figure 33. The diffusible auxin more than doubled with each ten day period in the development of the plant. Light is an important factor in auxin formation, although not a simple one. There is some confusion concerning the necessity of light for auxin formation, but in general it would appear that green plants do require light for this function, whereas excised plant parts grown on an organic medium or seedlings with a stored food supply can produce auxin in the absence of light. LiJ 3 > O LlI. 70 HRS. TIME IN LIGHT Fig. 35. The reappearance of auxin in tobacco apices when the plants were placed in light (8000 ergs/cmVsec.) (Avery et al, 1937). An excellent quantitative study of the relationship of light to auxin fonnation was carried out by Avery et al (1937) using tobacco plants. They observed that the auxin diffusible from the apices of tobacco plants diminished rapidly when the green plants were held in darkness (figure 34). Using this information, they then developed a technique for following the resurgence of auxin formation after starva- tion in the dark. Exposure of the plants to ten hours of light was sufficient to allow the reappearance of auxin, and a quantitative in- crease with greater duration of light was observed (figure 35). This. 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 Leopold, A. Carl (Aldo Carl), 1919-. Berkeley, University of California Press
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