SEEDLING GROWTH OF CATAWBA RHODODENDRON .1. TEMPERATURE OPTIMA, LEAF-AREA, AND DRY-WEIGHT DISTRIBUTION

Catawba rhododendron (Rhododendron catawbiense Michx.) seedlings of tw o provenances, Johnston County, N.C. (35 degrees 45'N, 78 degrees 12'W , elevation = 67 m), and Yancey County, N.C. (35 degrees 45'N, 82 degr ees 16'W, elevation = 1954 m), were grown in controlled-environment ch ambers for 18 weeks with days at 18, 22, 26, or 30C in factorial combi nation with nights at 14, 18, 22, or 26C. Shoot and root dry weights a nd total leaf areas of seedlings of the Yancey County provenance (high elevation) exceeded (P less than or equal to 0.05) those of the Johns ton County (low elevation) provenance at all temperature combinations. Leaf area was maximal at 22/22C, 18/26C, and 22/26C and minimal at 30 /14C (day/night). Shoot dry weight responded similarly. Root dry weigh t decreased linearly with increasing day temperature, but showed a qua dratic response to night temperature. Leaf weight ratio (leaf dry weig ht : total plant dry weight) increased, while root weight ratio (root dry weight : total plant dry weight) decreased with increasing day tem perature. Leaf weight ratio was consistently higher than either stem o r root weight ratios. Day/night cycles of 22 to 26/22C appear optimal for seedling growth.