Seasonal and diurnal expansion and contraction of fruits of forest trees

Seasonal and diurnal expansion and contraction of growing fruits of Acer rubrum L., Prunus serotina Ehrb., P. pensylvanica L., P. virginiana L., Quercus rubra L., and Corylus cornuta Marsh, var. cornuta were measured with modified Fritts dendrographs during the summers of 1966 and 1967. Throughout much of the summer the fruits exhibited recurrent shrinkage during the day and expansion at night. Fruit diameter fluctuations in 1967 were related to changes in vapor pressure deficit. Expansion of fruits generally occurred when vapor pressure deficit was decreasing or low and contraction resulted when vapor pressure deficit was increasing or high.