1. The history of plant tissue culture is outlined.
2. The technique of root cultures is reinvestigated from several aspects and some changes are incorporated for the present work.
3. The section of vitamin B1 as a root growth hormone is examined, and its presence is found to be closely correlated with the growth rate, rate of cell divisions, and extent of meristem in isolated roots.
4. A second growth factor of pea roots present in yeast extract is found not to be among the micorelements of plant nutrition nor among the amino acids.
5. Nicotinic acid is found to be the second growth factor of pea roots. With vitamin B1 it is capable of supporting a higher rate of growth for pea roots than can yeast extract.
6. Evidence is presented to show that inositol, phosphate, and optimum hydrogen ion concentration may have promotice effects on the growth of pea roots.
7. A number of experiments are described which indicate that it may be impossible to establish a clone of pea roots.
8. Preliminary experiments on the culture of excised anthers are described, and the high activity of embryo extracts on anther growth is noted.
