bar of osmotic pressure were, respectively, 0.576 +0.004, 0.570+0.004, 0.568 +0.004, and 0.562 ? 0.005. These sensitivity values for the separate couples are averages for determinations at five osniotic pressures. The standard errors measure the accuracy of proportionality between output, in microvolts, and osmotic pressure. The coefficient of variability of the voltage readings for five replicates of each of the KCl concentrations was determined for each of the thermocouples; the over-all average of these 20 coefficients was 0.5 percent. The highest variability occurred at the highest osmotic pressure for which the average coefficient of variability for the four junctions was 1.1 percent.The calibration of a hygrometer that makes use of evaporative cooling depends on atmospheric pressure. For a given osmotic solution in the sample chamber of the couples here described, the rate of change of sensitivity with change in atmospheric pressure is constant but increases as the osmotic pressure of the sample is increased. The increase in sensitivity for a 10-mbar decrease in barometric pressure is 0.00145, 0.00155, and 0.00160 %v, respectively, per bar of osmotic pressure, for standard osmotic solutions of 5, 10, and 20 bars. Correction for change of atmospheric pressure from the value at calibration will not often be needed, but barometer readings should be taken so that correction can be made if necessary.The physical condition of water in soil is usually specified in terms of equivalent membrane pressures, largely because measuring techniques employing membranes are available. With thermocouples which can be accurately calibrated in terms of relative pressure near saturation, it seems clear that the thermodynamic functions of free energy and activity will be more generally used for describing soil-water-plant systems.

No abstract

The effects of 22 herbicides on oxidative phosphorylation in mitochondria from cabbage (Brassica oleracea var. capitata L.) have been studied. Carbamates, phenoxyacids, 3,5-dimethyltetrahydro-l,3,5,2H-thiadiazine-2-thione (DMTT), N-1-napthylphthalamic acid (NPA), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), and 2-chloro-2-N,N-diallylacetamide (CDAA) inhibited phosphorylation to a greater extent than oxygen uptake in cabbage mitochondria. The compounds 1,2-dihydropyridazine-3,6-dione (MH), 2,2-dichloropropionic acid (dalapon), 2,2,3-trichloropropionic acid (hereinafter referred to as 2,2,3-TPA), sodium chlorate, and 3-amino-l,2,4-triazole (amitrole) at concentrations as high as 1 × 10–2 M did not have a large effect on oxidative phosphorylation in cabbage mitochondria. Respiration which was stimulated by 2,4-dinitrophenol (DNP) or adenosine diphosphate (ADP) was inhibited by 2,4-dichlorophenoxyacetic acid (2,4-D). Although 2,4-D did not affect Mg++-stimulated adenosine triphosphatase (ATPase), it inhibited an oleate-stimulated ATPase activity and the ATP-32Pi exchange reaction in cabbage mitochondria. The results suggest that 2,4-D may inhibit respiration in cabbage mitochondria by an effect on a reaction involved in coupling phosphorylation with electron transport.

No abstract