Leaf reflectance in the 0.40‐ to 0.75‐μm wavelength interval is influenced primarily by the pigments chlorophyll and carotenoid. However, the literature contains very few references to the relation between reflectance from leaves and their carotenoid content. Our objectives in this study were to determine which of three wavelengths in the visible spectral region best related leaf reflectance to total chlorophyll and carotenoid concentrations, and the relative effect of these pigments on reflectance. Hemispherical reflectances of single leaves at each of the 0.45‐, 0.55‐, and 0.67‐μm wavelengths for cantaloupe (Cucumis melo L. cv. reticulatus Naud.), corn (Zea mays L.), cotton (Gossypium hirsutum L.), cucumber (Cucumis sativus L.), head lettuce (Lactuca sativa L. cv. capitata L.), grain sorghum (Sorghum bicolor (L.) Moench), spinach (Spinacia oleracea L.), and tobacco (Nicotiana tabacum L.) were regressed on each crop's leaf total chlorophyll and carotenoid concentrations. The crops were grown in sand culture, and their leaf pigment concentrations were varied by supplying N at rates of 14, 28, 84, 140, and 196 ppm to a basic nutrient solution. Hemispherical reflectance of leaves was inversely related to each crop's leaf chlorophyll and carotenoid concentrations. However, of the three wavelengths tested, the 0.55‐μm wavelength seemed superior for individually relating the two pigments to leaf reflectance. The independent effects of carotenoid on hemispherical reflectance were small and generally not statistically significant, whereas the independent effects of chlorophyll while small were generally significant. The combined effects of these variables were highly significant and accounted for 39 to 95% of the reflectance variability. This study indicated that even though including carotenoid with total chlorophyll measurements improved the correlation of reflectance with pigment concentration, satisfactory results would be obtained by chlorophyll analysis alone.

Optical parameters (absorption coefficient k, infinite reflectance R ., scattering coefficient s) are tabulated for seven wavelengths and analyzed for statistical differences for 30 plant species. The wavelengths are: 550 nm

No abstract

Summary. The effect of ethylene on the uptake, distribution and polar transport of Cl4 from indole-3-acetic acid-2-C'4 and naphthalene acetic acid-i-C'4 in tissue sections was studied. Test species were cotton (Gossypiumn hirsutumit, L.) and cowpea (Vignla sinlellsis, Endl.). Generally, incubation of tissue or initact plants with ethylenie reduced the degree of polar auxin transport. Ethylene inhibited the movemiient of both auxins in stem tissue and IAA in petiole tissue of cotton. The effect of ethylene onl auxini mlovemelnt in cowpeas was more complex. Ethylene apparently inihibited transport in younlger petiole and stem tissue, but stimulated the process to a small but significant degree in basal petiole segments.Ethylene, in some experiments, reduced C14 (auxini) uptake. This reductioni was consistently smaller than the inhibition of transport. Effects upoll transport were observed when uptake was not different. Differenices in upltake declined as the period of inicubation with auxin was lengthened. but transport was inihibited for up to 23 hours.It is proposed that ethylemie may, through its effect on transport, cause localized shortages amid surpluses of auxiin whichi in tturn contrihute to symptonis now associate(l with the responise of senisitive species to ethylene.