1. Solutions of glucokinin and insulin, particularly those from which the easily dialyzable substances had been removed, increased the growth of roots and tops of young maize seedlings, as shown by comparisons with untreated seedlings grown in distilled water.
2. Strong solutions of crude glucokinin or of crude insulin repressed growth.
3. Seedlings from which the tips of the primary roots had been removed just before placing the plants in the test solutions made greater gains in both top growth and root growth than seedlings with uncut roots treated with solutions of the same strength. Control experiments showed that this difference in growth was not the result of cutting the roots, and that crude glucokinin and crude insulin contained several substances some of which were more readily absorbed by the plant than others.
4. Purification of crude glucokinin and crude insulin by dialysis showed that the residue of relatively non-dialyzable substance was the growth-promoting fraction.
5. The dialysate of crude glucokinin contained at least three types of material, one of which repressed growth.
6. Ammonium sulfate, one of the possible impurities of glucokinin, repressed the growth of seedlings but did not produce the other changes in metabolism shown by seedlings treated with dialysate of onion glucokinin.
7. The endosperm of plants treated with growth-promoting solutions of purified insulin did not lose weight as rapidly as the endosperms of untreated plants, indicating that the treated plants made their greater gains in growth by more efficient utilization of the endosperm, or as a result of greater photosynthetic activity, or by a combination of these.
8. Experiments with albino seedlings suggested that the greater gain in weight made by plants treated with insulin was the result in part of increased photosynthetic activity.