Selected Works pp. 166-167 (1949)
Ivan Michurin

Here I find it appropriate to state, that despite the general belief in the difficulty of crossing plants belong to different species—and more so—in different genera, I have lately obtained quite a number of interspecific hybrids and a few cases, although rather doubtful ones, of intergeneric hybrids. The latter may have been obtained without the fusion of the parent gametes but as the result of the direct influence of the fecundating source (the pollen) on parts of the maternal plant other than the egg cell, thus calling forth the parthenogenetic development of the latter. As to the degree in which the genes of the parents are transmitted to the hybrids, my observations have led me to believe that not only does the individual vigour of each plant type play an important role, but also that the age of each plant and the age of the species as a whole are of significance. Thus, the greater the stretch of time that a given species has been existing in its place of origin under similar soil and climatic conditions, the greater will the degree of hereditary transmission be which the individual plants belonging to this species possess. Furthermore, the older the plant chosen as a progenitor, the greater is the force with which it transmits its genes to the offspring, and conversely, if the plant is young, in its first years of bearing, and particularly if it is a hybrid of recent origin, its hereditary power reaches a minimum. Even artificial weakening such as preliminary transplantation or excessive drying of one of the parent plants lead to the reduction of this power.