During the 1978 growing season a growth analysis was performed on potatoes (Solanum tuberosum L.) planted on 2 February and 14 March. Two cultivars, Monona and Sebago, were studied. During the winter of 1979 a thermogradient analysis of Sebago growth was conducted. The objective of these studies was to provide data for the development and validation of a mathematical crop growth and development model. During the summer and fall of 1979 such a crop model was written in the GASP IV simulation language. The purpose of the crop model was to elucidate the effects of temperature on assimilate partitioning. The results of the crop growth and development model indicated that the primary effect of soil temperature was through a direct regulation of the tuber growth rate which had a 15° C temperature optimum, A high potential tuber growth rate stimulated photosynthesis; so a secondary effect of soil temperature was on net daily photosynthesis. The major effect of air temperature was its influence on the tuber initiation date. Air temperature and tuber initiation rate were inversely related. The air temperature also affected the rate of canopy senescence with warm temperatures speeding leaf drop and reducing the crop growth rate. The main weakness of the model was that light interception data were input rather than generated by the model itself.