Abscission of Marcescent Leaves of Quercus palustris and Q. coccinea

Abstract

An investigation was made of the abscission phenomena associated with the marcescent leaves of Quercus palustris and Q. coccinea. Small sections of stem with the petiole attached were collected and studied weekly. Most leaves remained on the trees during the winter. The phenomena accompanying abscission proved to be similar in both spp. The first change noted was the formation of a layer of lignified cells in the distal portion of the petiole base. This occurred 3.5 and 2 months before leaf-fall was complete in Q. coccinea and Q. palustris. respectively. It was found that the separation of the petiole from the stem occurred 1-2 layers of cells below this lignified layer. The first leaves shed by both spp. dropped as a result of mechanical forces such as wind and the wt. of the blade and petiole. The leaves which dropped a few days prior to the completion of abscission abscised as a result of the collapse and separation of the cell walls in the separation layer.