Pollen does not provide fertilization. This may be due to sterility of the pollen grain or egg cell. Also, pollen may not be able to penetrate the style due to incompatibility between two varieties. This may be due to nutrition and low temperature. The more seeds present in the fruit, the bigger the fruit, and and the more symmetrical the shape.
Seed numbers have a profound influence on both the size and shape of the fruit.
No apple variety is sufficiently self-fruitful to be dependably productive when planted alone. Therefore, if a triploid variety is to be planted, a pollen variety must be planted with it, then a second pollinizing variety must be planted to pollinize the pollinizing variety. The same is true for McIntosh, Rome, Golden Delicious, etc. In their off years, when they fail to bloom, there will be no pollen supply to pollinize the annual varieties. Is is suggested to set a third variety in such blocks.