Pollen tube growth and ovule vitality were studied in sour cherry cv. Čačanski Rubin in several combinations of pollination under field and laboratory conditions at constant temperatures at anthesis. On the basis of these studies, which revealed the existence of a year-to-year variation in fertility, a mathematical model of quantitative growth characteristics of pollen tubes in the pistil and the duration of ovule vitality has been developed. The analytical evaluation of the efficacy of pollen tube growth in the style and ovary and the ovule viability by means of the multiple regression model offers great possibilities in defining the area of the optimal combination of the factors studied, as well as the estimation of the moment at which they could take place. The possibility of a comparative analysis of the mentioned factors for defining the effective pollination period IS especially important, i.e. the prediction of single and combined effects of these factors ON the changes in the fertility of cv. Čačanski Rubin, depending on the temperature conditions in the field.