Histological and Cytological Responses of Roots to Growth-Regulating Substances

Abstract

Bulbs of Allium cepa, Tulipa (vars. Louis XIV and Jno. Ruskin) and Narcissus (var. Paper White) were rooted in containers of balanced nutrient soln.; and when the roots were sufficiently long, they were transferred to vessels containing nutrient soln. to which growth-regulating chemicals had been added in concs. of 10 or 20 ppm. After treatments of 24-72 hrs. the bulbs were rinsed with dist. water and returned to untreated nutrient soln. Roots were killed and fixed at regular intervals up to 216 hrs., sectioned, and examined. Following treatment the roots ceased elongation. There were terminal enlargements or tumors formed on all roots except those of tulip, the latter showing little or no enlargement. Histological examination showed the tumors to be formed by enlargement of the cortical cells and not by the increase in the number of cells. Roots of Allium formed numerous primordia, some of which emerged as lateral roots which were short, enlarged, and which had primordia. Roots of Narcissus and Tulipa did not develop primordia or secondary roots, though those of Tulipa showed proliferation of the pericycle and endodermis which might indicate potential primordium formation. Cell polarity was altered in many cases, giving rise to many radial, tangential, and diagonal cell divisions. Mitosis was promoted in mature tissues as far as 16 mm. from the root apex. The development of multinucleate cells was not brought about, and the number of polyploid cells observed was within the limits of those occurring in control material.