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Influence of Photoperiod on Microsporogenesis in Cosmos sulphureus Cav. Var. Klondike
Grace C. Madsen
Vol. 109, No. 2 (Dec., 1947), pp. 120-132
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2472605
Page Count: 13
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1. Experimental groups of Cosmos sulphureus Cay. var. Klondike were given photoinductive cycles of 8 hours of light and 16 hours of darkness for 6, 7, 8, 10, 12, and 14 days. The groups were then divided into three lots each, which were given differential postinductive photoperiods of 14, 19, or 24 hours. 2. Controls were run on natural and 8-hour photoperiods; both of these lots flowered profusely. Three other controls run continuously on 14-, 19-, and 24-hour photoperiods did not flower. 3. Flower buds were collected and fixed Successively from all groups. These provided a normal series for floral and meiotic development through pollen formation and material for the study of abnormalities induced by the experimental photoperiods. 4. The markedly suppressed buds of Cosmos, usually surrounded by long foliaceous outer bracts and inner inhibited ones, showed no differentiation of floral parts or sporogenous tissue. Less retarded reproductive structures produced floral tube, sporangial wall, a black-line tapetum, and sporogenous cells with little or no cytoplasm. These sporocytes did not initiate the prophases. 5. In plants in which retardation was less marked, various abnormalities occurred, such as degeneration of tapetum, plasmodial masses derived from sporogenous tissues accompanying the normal stages, lagging of chromosomes and the failure of some of them to be included in the microspores, and degenerating cytoplasm in the microspores. 6. No pollen which appeared to be morphologically normal occurred in the anthers of flowers in which tapetal cells did not form a locular matrix. 7. Although a quantitative record of buds of the experimental lots clearly shows a reduction in total reproductive activity in relation to reduced photoinduction and to increased length of the postinductive photoperiod, it is cytologically impossible, to draw lines of demarcation between the lots.
Botanical Gazette © 1947 The University of Chicago Press