Demonstration of Photoperiodic Ecotypes in Liriodendron and Quercus

Seedlings of Liriodendron tulipifera responded very sensitively to daylength treatments in growth chambers. A certain daylength (6-hour night) inhibited northern but not southern seedlings. The same was true with seedlings of Quercus macrocarpa but the inhibition occurred under very short days (12-hour night) and the responses were smaller. In this species the onset of dormancy was controlled more strongly by the endogenous growth rhythm. The different photoperiodic responses appear to be an adaptation mechanism in these as well as in other species studied earlier. The responses could conceivably function for reliable timing in the alternation of growing and dormant stages.