Three year-old Delaware grapes potted were removed from the open field into the glass houseat 35th day(July 12) and 55th day(August 1) after anthesis, respectively, in order to be exposed to the high day-temperature, and the treatments were continued, till the last harvest time (September 4). All windows of the glass house were closed in day time and open at night, but if necessary, a part of them were opened in day time to keep out the overrise of room temperature. The daiy maximum temperature inside of the glass house was 4.7-2.0℃ higher and the daily mean temperature in day time inside of it 3.4-2.8℃ higher than those in the open.(Table 1 and 2)
1. The high day-temperature treatments inhibited the coloration and maturation of the grapes, in which the increase of anthocyanin was mostly affected, followed by the berry growth, the increase of soluble solid and the decrease of chlorophyl, and the decrease of acid was leastly affected. Then, the earlier the beginning of the treatment, the stronger was the influence of it on them. (Table 3,4 and Fig. 1)
2. The rates of apparent photosynthesis and the sugar contents in the leaves of the high day-temperature plots were less than those of control plot. But in total carbohydrate, there was a little difference between these plots. (Table 5 and 6)
3. It seems that the delayed coloration and maturation of Delaware grapes observed in the high day-temperature condition in summer mainly result from the disorder of carbohydrate assimilation in leaves induced by the temperature. The coloration, however, might also be affected directly by the high day-temperature, for the anthocyanin formation in skin was mostly inhibited under the condition as compared with the other acts of maturating.