Image from http://www.pdimages.com
A sperm (with tail) trying to fertilize the egg (the partially seen sphere).
Fertilisation (British English), also spelled fertilization (American English),which is less ambiguously referred to as syngamy, is the process of a sperm fusing with an ovum, which eventually leads to the development of an embryo.
To deliver the sperm to female, the male inserts his external sexual organ into the opening to vagina, the passage into the female's sexual organ. (This process is a part of copulation.) Once the male ejaculatess, a large number of sperms swim toward the ovum. One of them penetrates the ovum's coat, and the ovum is fertilized and the female is pregnant.
After the female part of the flower is pollinated, pollen grains attempts to travel into the ovary by creating a path called "pollen tube." The pollen tube does not directly reach the ovary in a straight line. It travels near the skin of the style and curls to the bottom of the ovary, then near receptacle, it breaks through the ovule and reaches the ovum to fertilize it. After being fertilized, the ovary start to swell and become a fruit.
With multiseeded fruits, multiple grains of pollen are necessary for syngamy with each ovule. The process is easy to visualize if one looks at corn silk, which is the female flower of corn. Pollen from the tassel (the male flower) falls on the sticky external portion of the silk, then pollen tubes grow down the silk to the attatched ovule. The dried silk remains inside the husk of the ear as the seeds mature, so one can carefully remove the husk to show the floral structures. The development of the flesh of the fruit is proportional to the percentage of fertilized ovules. For example, with watermelon, about a thousand grains of pollen must be delivered and spread evenly on the three lobes of the stigma to make a normal sized and shaped fruit.
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