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Abscission of Marcescent Leaves of Quercus palustris and Q. coccinea
Robert W. Hoshaw and Arthur T. Guard
Vol. 110, No. 4 (Jun., 1949), pp. 587-593
Published by: The University of Chicago Press
Stable URL: http://www.jstor.org/stable/2472663
Page Count: 7
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1. There is no well-defined separation zone at the base of the petiole in either Quercus palustris or Q. coccinea. The cells of the base appear to be histologically the same as those of adjacent tissues. 2. The processes accompanying abscission are found to function within a greenish area of living tissue at the base of the petiole of a marcescent leaf; the remainder of the petiole and the blade are dead. 3. A lignified layer consisting of from four to twelve tiers of cells forms in the petiole base. This lignified layer was observed early in January in Q. coccinea and 6-7 weeks later in Q. palustris. 4. The separation layer is located one to two cells below the lignified layer and includes four to five tiers of cells. 5. The process of abscission involves the separation of some cells along the plane of the middle lamellae, while other cells separate by a passive breaking of the cell walls at right angles to the middle lamellae. 6. No cell division was observed during the abscission process. 7. During the abscission of the last leaves to fall the cell walls of the separation layer collapse, allowing the petiole to separate easily. The first leaves drop as a result of mechanical forces, such as wind and the weight of the blade and petiole. 8. The greater portion of leaves of both Q. palustris and Q. coccinea abscise over a relatively short period of time. Leaf-fall in Q. coccinea was more rapid and uniform than in Q. palustris. 9. Crystals of calcium oxalate were present in all the material examined. These crystals appeared to be distributed through all tissues, including those in the separation layer. 10. A high percentage of the leaves of Q. coccinea dropped as a result of the breaking of the petiole. Some leaves of Q. palustris also fell as a result of broken petioles. The petiole stubs dropped when the buds swelled.
Botanical Gazette © 1949 The University of Chicago Press