. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Natural auxins soaking period in MnS04-|-H20 (1 mg/l.) was adopted for coleoptile sections and a 1-hour presoaking period in glass-distilled water for the inter- node sections, the latter being maintained breaking the surface on stretched cheese-cloth. In a given plant extract, the quantity of auxin is generally small. The problem is how to make the best use of it to get the maximum growth response. If we have,
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Natural auxins soaking period in MnS04-|-H20 (1 mg/l.) was adopted for coleoptile sections and a 1-hour presoaking period in glass-distilled water for the inter- node sections, the latter being maintained breaking the surface on stretched cheese-cloth. In a given plant extract, the quantity of auxin is generally small. The problem is how to make the best use of it to get the maximum growth response. If we have, let us say, 0-01 y of lAA, is it better to dissolve it in 1 of assay solution, or in 10 ? It is known (cf. Schneider, 1938) that ^ ^ 1^01ume M C 0-5 -K^- 0-5 1-0ââ >--i-o Z-0 ââ â S-0. 180 leo mo 120 r 100 -^ 80 GO <fO % f 10 f-o 100 100 Total amount of lAA 1000 9000 10,000 yxlO'^ Figure 13. Effect of the volume of solution on the growth of oat first internodes [M) and coleoptiles (C). The total amounts of lAA indicated on the abscissa {logarithmic scale) were dissolved in either 0-5, 1-0, or 2-0 {when using first internodes) or 0-5, 1-0, or 5-0 {when using coleoptiles) of the usual buffer solution plus 2 per cent sucrose and 0-1 per cent Tween 80. controls in distilled water tend to grow less in large than in small volumes, presumably because of the dilution of a food factor. This effect can be ruled out (1) by presoaking the sections in large volumes of solutions before the actual assay and (2) by adding a food factor, such as sucrose, to the assay solutions. Experiments in which these precautions were taken showed repeatedly that the growth of the controls is the same in 0-5 or 5 , and that growth of both coleoptile and internode sections in lAA plus sucrose and buffer does not change appreciably according to the volumes used {Figure 13), provided, of course, that no evaporation takes place during the assay with 0-5 It should
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