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Plants of eastern redbud (Cercis canadensis) from seed collected from native trees throughout the natural range show considerable morphological variation. Characteristics usually associated with xeric conditions, such as increased pubescence, thicker and smaller leaves, and efficient stomatal geometry, are correlated with evapotranspirational trends over the natural range, reaching extremes in western populations. Photoperiodic growth response, time of initiation of dormancy, rate and extent of acclimation, and chilling requirements of dormant buds also vary over the natural range. Plants of southern origin continue to grow under shorter photoperiods than northern plants, and are slower to enter dormancy under short days. Plants of northern origin acclimate more rapidly than southern plants. Degree of acclimation in a fixed time is correlated with climatic parameters as well as latitude and, in the case of first—stage acclimation, longitude as well as latitude. Chilling requirements for breaking bud dormancy increased with latitude, with Florida plants showing no dormancy or chilling requirement.

Cold—hardiness of stem sections of white ash (Fraxinus americana L.) from 10 geographic origins in eastern North America, growth in a provenance planting in south Michigan, was determined by controlled freezing. Northern plants were more cold—hardy than southern plants in early and midwinter, but differences disappeared by early spring. Substantial variation in cold—hardiness was found among trees within each origin. Multiple regression of killing temperatures on latitude, longitude, elevation, average annual minimum temperature, and annual frost—free period proved useful in predicting cold—hardiness, and may be useful in forecasting performance of trees in locations removed from their sites of origin.

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