Results of histochemical tests for peroxidase activity in seven species of grasses have been reported. The root epidermis of the festucoid grasses is characterized by rows of alternating shorter hair and longer hairless cells which can be recognized throughout their development. Peroxidase activity occurred in all the growing cells, but intensified reactions were observed in the hair cell initials in the bases portion of the elongation zone. The panicoid species have a root epidermis in which any cell seems capable of producing a root hair, and in these species all cells in the growing regions showed equal peroxidase activity. The close correlation between the differentiations of enzymes and cell types implies that physiological changes occur long before the morphological maturation of the tissue.