Evolution of CO2 into CO2-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O2-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O2-free air nor any evolution of CO2 in CO2-free air at any of the temperatures.

Translocation of assimilated(14)C from the leaves of different species varied both in the rate of export and in the total percentage moved out. Those species which are known to have high photosynthetic rates, such as the tropical grasses sorghum and millet, exported 70% or more of the assimilated(14)C during the first 6 h after assimilation, compared to values of 45 to 50% for tomato, castor bean,Nicotiana affinis and soybean.The compounds in which the(14)C was retained in the leaves varied from species to species. Except for castor bean only small amounts were retained in sucrose, with generally much higher amounts in fructose, glucose and malic acid. Most of the(14)C was retained in the ethanol-insoluble fraction.

Severe injury was observed on white cedar and several species of pine adjacent to highways in southern Ontario in the spring of 1970. Foliar injury, measured quantitatively as the ratio of brown to total leaf tissue, and foliar levels of sodium and chloride higher than background levels occurred on trees up to 120 m from the highway, particularly on the downwind side of the highway, on the windward side of the tree, and on trees in exposed positions. Injury and foliar levels of sodium and chloride progressively declined at greater distances from the highway. For a given level of sodium or chloride more damage occurred on the windward side than on the sheltered side of the tree. The data suggest that salt applied to highways in the winter is whipped up in a spray by traffic, blown onto vegetation, and contributes to leaf injury. Wind and lower than average winter temperatures also appeared to contribute to the injury observed in 1970. At similar foliar concentrations of sodium and chloride white pine showed twice as much injury as white cedar. Of the pines close to the highway, damage was greatest on white pine and red pine, intermediate on Scots pine, and least on Austrian pine and Mugo pine. At similar levels of damage all pines contained similar foliar levels of sodium and chloride.