Experiments on Photoperiodism, Dormancy, and Leaf Age and Abscission in Sugar Maple

Abstract

1. A seedling population of sugar maple (Acer saccharum Marsh.), derived from two native seed trees in southeastern Wisconsin, was grown for 7 years (1941-1947) in pots in the University of Chicago greenhouses and gardens. The experimental variables were mainly length of photoperiod and amount of winter chilling, studied particularly in relation to leaf senescence and abscission, onset and completion of bud rest, budbreak, and amount of terminal growth. 2. It was concluded that in this species the loss of green color and leaf abscission under natural conditions are basically conditioned by the naturally decreasing autumnal photoperiod. In the various years and experiments leaves expanding from as early as February to as late as August were mostly abscised in October and November if the plants were maintained on natural photoperiod, either indoors or out. Chronological age of leaves had a limited relation to time of senescence and abscission, youngest leaves persisting a few days longer. Constant photoperi...