A study to determine "norms" for the tapping of Hevea brasiliensis is being carried out in Cote d'ivoire. This is aimed at defining an age and minimum circumference for the opening of Hevea which takes into account the notion of physiological maturity. The modelled vegetative growth curve is a sigmoid with a gradient change point at the third phase that is a plausible solution to the problems of this study. Analysis of growth dynamics shows that this point hardly varies, irrespective of the growth class of the clone, and takes place at the sixth year after planting. In addition, several observations on the growth of Hevea under different conditions lead to the proposal of a minimum tapping circumference linked with the growth class, thus combining the notion of age and size. This study finally shows that economic objectives are not always adequate for some of the requirements for the development of plants.