Abstract: This paper deals with the function of chloroplasts from the mesophyll cells of winter wheat Nongda 311 as a continuation of our previous studies on the leaf cells of the same species. Samples of leaves were taken for electron microscopy and photosynthetic determinations. It is found that the ultrastructures of chloroplasts from different ranks of leaves very in complexity in an ascending order. The stroma of chloroplasts from the upper-ranked cells are heavily stained as shown by their high content of ribosomes and high consistancy of the mobile phase. The grana lamellae in the flag leaf chloroplasts are thickly stacked against a few disks in the grana of 5 th leaf. The rate of Hill reaction and photophosphorylation of the flag leaf is higher than that of the 5th leaf. The mitochondria in the flag leaf cells are large and numerous as compared to these from the 5th leaf. The respiration of the flag leaf is nearly two fold higher than that of the 5th leaf. To sum up our data, we see that the close association between structure and function has gone through a series of changes from the simple to the complex. It is our task to reveal the changes in detail and take measures to regulate the changes, for it is of practical importance.