Effects of Root-Growth Hormones on the Meristem of Excised Pea Roots

Abstract

1. Deficiencies of the root-growth hormones vitamin B1 and nicotinic acid in cultures of excised pea roots have visible effects in the meristem. 2. The deficiency of either substance results in a decrease in the growth rate and eventual complete cessation of growth. This is accompanied by reduction in the length of the meristem, decrease in the number of cell divisions in the meristem, as well as reduction of the total length attained by the cells as they mature. 3. Roots deficient in nicotinic acid become thin. This is accompanied by reduction of the diameter of the root cells and of the number of columns of cells in the roots. 4. The meristems of roots deficient in vitamin B1 become only slightly smaller in diameter in the course of 4 weeks, but their growth rate declines more rapidly than does that of roots deficient in nicotinic acid. The mature portions of these roots develop irregular thickenings.