Tomato plants were grown in sand culture in glass inclosed chambers and humidity was maintained at 85 per cent in all cases. Sunlight and carbon dioxide supply varied but at any given time were the same for each temperature treatment. The following relative differences which occurred in growth and metabolism at 55⚬, 70⚬, and 95⚬ F. were brought about as the result of differences in temperature. 1. Temperature 55⚬ F. (13⚬ C.).-At this temperature carbohydrates, especially starch, accumulated in large quantities, indicating beyond question that assimilation of carbon dioxide exceeded respiration. Nitrate was absorbed instantaneously, and in about five hours was present in high concentration throughout the plant and remained high. Nitrate was assimilated (synthesized to organic nitrogen) very slowly and the plants were very low in nitrate reducing material (9). Accordingly, carbohydrates were high even in nitrate supplied plants, as there was little utilization of carbohydrates in protein synthesis. Externally the plants were yellowish green, owing to a low chlorophyll content and comparatively few and poorly developed chloroplasts. The veins and stems were purplish, from the presence of anthocyanins. The stems were hard and woody and the cell walls thick. This was true even of plants supplied with nitrate, although these conditions were accentuated in plants lacking nitrate. 2. Temperature 70⚬ F. (21⚬ C.).-Plants lacking an external nitrogen supply were not so high in carbohydrates as comparable plants at 55⚬ F., and exhibited symptoms of protein deficiency in less degree. Nitrate absorption was apparently instantaneous and translocation of nitrate was slightly more rapid than at 55⚬ F. The plants were high in nitrate reducing material (9) and assimilation of nitrate was rapid, hence there was a comparatively high concentration of carbohydrates in plants lacking nitrate as compared with those receiving nitrate. Plants supplied with a complete nutrient solution were moderately high in carbohydrates, contained an abundance of elaborated nitrogen, were dark green, rather succulent, and grew vigorously. 3. Temperature 95⚬ F. (35⚬ C.).-Plants with no external nitrogen supply as well as those with complete nutrient rapidly decreased in carbohydrates, indicating that respiration exceeded carbon dioxide assimilation at this temperature.4 Accompanying decrease in concentrations of carbohydrates, there was a breaking down of complex proteins to simpler forms of organic nitrogen, accelerated growth for a few days, and death of the plants. Nitrate absorption was apparently instantaneous and translocation of nitrate was a little more rapid than at 55⚬ or 70⚬ F. At first nitrate assimilation and reducase activity (9) were extremely high and the external response occurred much sooner than at 70⚬, but after four or five days nitrate assimilation practically ceased and the nitrate supplied plants grew much more slowly than at 70⚬ F. Because of carbohydrate utilization in protein synthesis, as well as in respiration, the plants which received nitrate lost carbohydrates more rapidly and died sooner than those with no external nitrogen supply. During the early stages of 95⚬ treatment, the plants receiving a complete nutrient solution grew rapidly and were dark green, although spindling. After a few days there was disintegration of chloroplasts, the newly developed leaves contained few and small chloroplasts (9), and the plants as a whole were soft, yellowish green, mottled, and practically free of anthocyanin pigmentation.