. Auxins and plant growth. Auxin; Plant growth promoting substances. 206 Auxins in Agriculture This has led to the generalization that the ratio of carbohydrate to nitrogen should be high for optimum rooting (Kraus and Kraybill, 1918; Pearse, 1943). The reports of many workers that nitrogen is detrimental to the rooting of cuttings ( Knight, 1926) undoubtedly are explained by the requirement for an abundant supply of carbo- hydrate in proportion to the nitrogen. It is interesting to notice that in replacing the stimulatory effect of leaves, van Overbeek et al (1946) obtained the best resul
. Auxins and plant growth. Auxin; Plant growth promoting substances. 206 Auxins in Agriculture This has led to the generalization that the ratio of carbohydrate to nitrogen should be high for optimum rooting (Kraus and Kraybill, 1918; Pearse, 1943). The reports of many workers that nitrogen is detrimental to the rooting of cuttings ( Knight, 1926) undoubtedly are explained by the requirement for an abundant supply of carbo- hydrate in proportion to the nitrogen. It is interesting to notice that in replacing the stimulatory effect of leaves, van Overbeek et al (1946) obtained the best results with forty times as much sugar as ammonium sulphate. The rooting response to auxin is a quantitative one. The quanti- tative characteristic of the response can be seen in the data shown in figure 89. The use of auxin concentrations higher than optimum re- sults in a reduction of rooting, but the evidence available suggests that this reduction may be owing more generally to the inhibition of growth of the root primordia rather than to a reduction in number of primordia formed. It is evident that auxins stimulate the formation of roots by an interaction involving organic materials in the plants, particularly car- bohydrates and nitrogenous materials. This interaction apparently controls the basic step of morphological differentiation at the cellular level. + Rough Lemon o^Cherimoyo Trifolata. 0 200 400 600 800 MG/L CONG. OF AUXIN Fig. 89. The quantitative stimulation by auxin of rooting in cuttings of three varieties of citrus. The auxin used was indoleacetic acid (Biale and Halma, 1937).. 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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