Histological Variations in Cosmos in Relation to Photoperiodism

Abstract

Plants of Cosmos sulfureus var. Klondike required a stimulus of 7-10 short days (8 hrs.) to bring them into flower, even if subsequently treated with long days. At low light intensities 71/2-hr. days tended to produce "vegetative flowers." The change of the primordium from foliar to floral was preceded by an accumulation of carbohydrate and protein in the stem tip and a disappearance of the same in the stem base. The total material stored was lessened by 1% per day. A diurnal fluctuation of glutathione in the stem tip occurred until the primordium became floral, thereafter it remained higher than in the vegetative controls. Asparagine was somewhat higher and ammonium was somewhat lower in the stem tip at the time of flower-bud formation. Microchemical as well as macrochemical analyses were made.