Abstract: Using the instrument developed by ourselves，the diurnal changes of tomato’s leaf thickness were acquired，which reduced around midday and increased in the morning as well as evening. In order to investigate the reason for this change，the comparison dissection analysis was carried on by the paraffin section with the samples continuously collected at the same time interval. The results indicated that the palisade tissue presented a ‘loose-close-loose’ phenomenon from dawn to dusk. Although there was no obvious change in the arrangement of the spongy tissue，the change of leaf thickness was consistent with the proportion of spongy tissue，which indicated that the spongy tissue’s volume directly affected the value of leaf thickness.

Key words: tomato, leaf thickness, paraffin slice, comparative anatomy