The Biosynthesis of C13 Compounds

1. Starch, containing 7.05 atom per cent C(13) excess has been produced in the mesophyll cells of bean leaves, starting with C(13)O(2) containing 7.26 atom per cent C(13) excess. Approximately 67 per cent of the C(13) taken up by the leaves was determined in the starch fraction. 2. The soluble carbohydrate, containing 6.72 atom per cent C(13) excess, accounts for approximately 23 per cent of the C(13) taken up by the leaves. The remainder was principally in the coarse tissue fragments fraction (9.73 per cent of the C(13) utilized). 3. The apparatus and procedures used in this experiment are described.