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Abstract

Mature female Maidenhair trees (Ginkgo biloba L.)have been observed to produce seed dispersal units in some years and none in other years. A temperature and/or photoperiod flowering threshold is suggested. Daily temperatures and daylengths at five Ginkgo sites in continental U.S. for January-April 1964-1974 were evaluated. A computer program was designed to estimate daily photothermal equivalent (PTE = temperature and photoperiod), and the magnitude and duration of the PTE in relation to a series of photothermal constants. Use of the data from production and nonproduction years provided a mathematical model for prediction of dispersal unit production. The model was tested with environmental data for additional sites recorded in the botanical literature.

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