It has long been known that when the pollen reaches the stigma, it produces a pollen tube which penetrates to the ovule. In 1830 Amici observed that the pollen tube had reached the ovum, but was unable to establish the fact that they had actually united. In his opinion, the pollen tube simply stimulated further development. It only later became known that the pollen fertilised the ovum, the most important cell in the interior of the ovary. There may be one or more ovules in the ovary. An embryo sac forms in the ovule and, as the result of complicated cell divisions, 8 gametes form in the embryo sac. These are characterised by the fact that they have a chromosome number which is only half that of the somatic cells. Of these 8 cells, 4 are to be found at the lower pole of the embryo sac and 4 at the upper pole. In the following stage, one cell each from the upper and lower groups migrate to the middle and unite, so that the chromosome number of this united cell is the same as that of the somatic cells. This is referred to as the secondary nucleus. Three cell nuclei thus remain at the bottom and three at the top, each surrounded by a separate cell wall. Of the upper 3 nuclei, one forms the ovum and the other two are accessory cells. In general it is the ovum which if fertilised. After pollination the cell nucleus of the pollen tube divides into two parts in the course of growth, one forming the vegetative cell nucleus and the other the generative cell nucleus. The first develops the pollen tube, the material of which is later absorbed. The generative nucleus divides into two (G1 and G2), after which both migrate towards the ovum, with which G1 unites. This gives rise to the zygote, the first cell of the embryo, which contains a double quantity of chromosomes. After this first fertilisation, G2 moves on downwards into the embryo sac, where it unites with the secondary nucleus, producing an entity with a triple quantity of chromosomes. This then develops into the endosperm. Since the cell nucleus of the fertilised ovum also contains the cell nucleus of the pollen, and since the chromosomes of the cell nuclei are the carriers of the plant characters, the characters of both parents are to be found in the new embryo.
The result of fertilizing almond with apricot pollen (the fruit obtained had an almond seed with four kernels from which four plants developed.) Michurin: Principles and Methods (1934)