COMPARATIVE CYTOHISTOLOGICAL STUDIES ON INHIBITION AND PROMOTION OF STEM GROWTH IN CHRYSANTHEMUM MORIFOLIUM

Abstract

Sachs, R. M. (U. California, Davis), and A. M. Kopranek. Comparative cytohistological studies on inhibition and promotion of stem growth in Chrysanthemum morifolium. Amer. Jour. Bot. 50(8): 772‐779. Illus. 1963.—The present study with Amo, CCC, and Phosfon,3 3 substances which inhibit stem elongation, shows that all inhibit subapical cell expansion and division in Chrysanthemum morifolium var. ‘Indianapolis Yellow.‘ Furthermore, GA,3 in preventing the inhibition of stem elongation, maintains subapical activity at normal or greater than normal levels. For comparative purposes concentrations of the retardants and GA have been selected which completely prevent or promote the maximum rate of stem elongation. Phosfon causes complete inhibition of root growth and almost completely prevents dry matter accumulation in the tops. However, GA does not prevent such deleterious effects. Thus, GA and the growth retardants are mutually antagonistic only with respect to stem elongation and not to other aspects of growth. Furthermore, none of the retardants inhibits transverse stem growth; on the contrary transverse cell expansion and division in the subapical tissues are stimulated by the retardants, and as a result the stems of such plants are thicker than normal. GA not only prevents the thickening effect of the retardants, but, at the doses applied, GA‐treated stems are considerably thinner than those of the controls, having fewer and smaller cells across the pith, cortical, and vascular tissues. Apparently, then, there is a relationship between longitudinal and transverse growth in the subapical tissues such that if one is promoted, the other is inhibited.