Structure of Stems in Relation to Differentiation and Abortion of Blossom Buds

Abstract

1. Soybean, Salvia, Cosmos, and Xanthium, all short-day plants, initiate blossom primordia after different durations of exposure to short days. Soybean and Salvia require 9, Cosmos 12, and Xanthium 5 days of short-day treatment for the appearance of blossom primordia at the appropriate temperature and cultural conditions. Stock, a long-day plant (at a medium or cool temperature), requires approximately 18 days for the appearance of primordia. 2. In order that the blossom primordia may continue to develop, it is necessary to expose the plants studied (except Xanthium) to a favorable environment for a greater length of time than just the induction period. Xanthium requires an induction period of only 2-3 short days at a warm temperature for the initiation and development of blossom buds. One short day is sufficient for the initiation of staminate blossoms. 3. Alterations in the anatomical structure of the stem occurred early in the development of plants placed in an environment favorable to the formation of blossom primordia. The first indication of a change in structure was a decrease in the number of meristematic cells of the cambial zone. Associated with this was the simultaneous decrease in the formation of xylem and phloem cells and a thickening of the cell walls of the vascular tissue. The cambium generally remained somewhat active, giving rise to new xylem but little phloem. The most recently formed phloem was composed almost entirely of phloem parenchyma cells. The stems of flowering and fruiting plants had little or no meristematic tissue, and the walls of the cells had become greatly thickened. 4. Plants of soybean, Salvia, Cosmos, and stock exposed to an environment favorable to flowering for a limited time only, and then returned to conditions inducive to vegetative growth, soon showed renewed cambial activity and differentiation of vascular elements with the failure of the blossom primordia to continue development. Plants of Xanthium given 2-3 short days became reproductive regardless of subsequent treatment.

Abstract

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