Pear Hybrid
Ivan Michurin (1915)

I pollinated the flowers of Pyrus elaeagnifolia with the pollen of a well-known orchard variety of pear named Bessemyanka [Seedless].

Fruit and leaves of the pure species Pyrus elaeagnifolia are shown in the centre of Fig. [9]. A leaf of the Bessemyanka pear is shown in the left upper corner of the figure, while a leaf of the hybrid produced by a cross between these parental forms is shown on the right. When rearing the seedlings of all the three forms I observed that whenever they were given better nourishment externally in all their parts the hybrid seedlings invariably deviated towards the Bessemyanka type. The leaf blades became broader and had a glossy surface, the shoots became thicker and their bark acquired a colour resembling that of the shoots of Bessemyanka. On the other hand, if the seedlings were subjected to some hardship, such as replanting or the insufficient water supply in the beginning of the vegetation period due to summer drought, the leaves of the plants grew narrow and elongated in shape, their surface as well as the bark of the shoots became downy, the buds became more rounded, in a word, all the elements of their habit showed a distinct trend towards the maternal type of Pyrus elaeagnifolia (the hybrids did not hear any fruit as yet).

Fig. 9. Pyrus elaeagnifolia and its hybrid: a leaf of a Bessemyanka pear [left]; a twig with two fruits of Pyrus elaeagnifolia [centre]; a leaf of the hybrid seedling [right]

*pood = 16.38 kilograms
Similar phenomena have been recorded in hybrids from other crosses as well, whenever a cultivated variety was crossed to a wild species. When a cross was made between two different varieties belonging to the same species, lack of nutrition or a drought usually caused deviation of the hybrids towards the type of the older parental variety—the one of longer standing. I have also carried out numerous other experiments to determine the effect of the composition of the soil on the constitution of growing hybrid plants and each time I became convinced of the considerable influence exerted by this factor. This influence was particularly pronounced in those cases when I succeeded in providing for the hybrid seedlings such a soil that was closely similar in composition to that on which one of the two parental plant varieties involved in the cross had successfully developed for a long period of time, or, so to say, had been formed, whereas the type of the other parent had been developed on a soil of an entirely different composition. In almost all such cases the hybrid seedlings were observed to resemble in type the first parent. Thus, I used to order several poods* of soil to be brought from the environs of Vladimir to grow the hybrids obtained in crosses between one of our cherry varieties raised in the Samara steppe region (Prunus Chamaecerasus) and the Roditeleva cherry from Vladimir. The soil ordered was the very one on which the Roditeleva cherry—a well-known Vladimir variety of cherries—was grown in its native locality. Although by means of this substitution of soil I succeeded only in partly approximating the environmental conditions in which these hybrids were reared to those of the Roditeleva cherry's native habitat, nevertheless the few specimens of hybrid seedlings that were given a mixed soil containing a high proportion of the Vladimir soil, showed a pronounced trend towards the Roditeleva cherry and markedly differed from the rest of the seedlings brought up on the ordinary soil of our locality. And just to think that this result has been obtained in experiments, in which so many necessary conditions were missing! These hybrid seedlings ought really to have been planted in Vladimir, not in Kozlov, and grown in the native locality of the Roditeleva cherry, because (besides soil composition) other factors such as the composition of the subsoil, and of the subsoil water, the depth of the subsoil water table level, the lay of the site, the difference in the climatic conditions, etc., play an important role. And if even in the absence of the influence of these important factors the supplying of the native soil alone was enough to produce so marked a deviation towards one of the parental types, then how is it possible to make correct estimates of the proportion of plants in a hybrid progeny that would deviate towards one or the other parental type and of the degree of this deviation merely on the basis of the hereditary transmission of the latter's properties.