Principles and Methods (1929)
The age and health of the parent plants chosen for the crossing are of very great significance in practice. Young hybrid plants in their first bearings, or older plants that have been bearing for many years but which were weakened by a dry or unusually cold spring during the given vegetation period, possess a weaker individual capacity for hereditarily transmitting their properties, and, conversely, plants belonging to pure species and, particularly, wild forms in their prime, possess the greatest capacity of handing down their properties to the hybrids. Thus, for example, from the cross of the Crimean Kandil Sinap with the Siberian crab apple [Malus baccata Borkh.] hybrids were obtained with fruits the size of our ordinary orchard Kitaika [Malus prunifolia Borkh.], whereas the cross between Kandil Sinap with the seedlings of our orchard Kitaika in its first blossoming produced fruits of an excellent taste. In this case the maternal parent was the young seedling of the Kitaika, not the pure type of course, but a hybrid; this became evident later from the larger size of its fruit as compared with the ordinary size of the Kitaika. That is why its resistance properties were not transmitted with due intensity, and as a result the shoot ends of the seedlings obtained from this cross suffered from the frost. To eliminate this shortcoming the hybrids had to be placed once again under the influence of their female parent—Malus prunifolia Borkh.—by grafting cuttings of the seedling into the crown of the maternal tree, which soon gave the required degree of resistance to the new variety. This circumstance should he taken into consideration when choosing the parent plants.
It has been likewise remarked that flowers chosen for fertilization on the maternal plant, if placed nearer to the main vertical branches of the trunk, give better hybrids with larger-sized fruit but such that tend to deviate considerably in structure in the direction of the maternal plant, and, conversely, flowers on the horizontal branches, placed nearer to the periphery of the crown generally give hybrids with fruit of smaller size and such that deviate in the direction of the male parent. The shady side of the maternal plant yields hybrids of poorer quality as compared to the sunny side. This is particularly clearly expressed by the depth of the outer colouring of the fruit and by the amount of sugar in the pulp.