Sexuality : A source of hereditary variation
Before the development of light microscope in seventeenth century, the idea about sexuality in animals was based on speculation rather than facts. For instance W. Harvey (1578-1657) speculated that all animals arise from eggs and that semen only plays a vitalizing role. R. de Graaf (1641-1673) observed that the progeny would have characteristics of father as well as mother and, therefore, suggested that both the parents should contribute to heredity. He also studied the development of embryo to some extent, although the egg was discovered by Von Baer in 1828. However, A.V. Leeuwenhoek observed sperms of several animals in 1677 and also suggested their association with eggs.
Reproductive parts of plants were reported for the first time by N. Grew in 1682. Subsequently R. Camerarius in 1694 described sexual reproduction in plants for the first time. Camerarius is also known to be the first to produce a hybrid between two different plant species. It was, however, in 1717 that T. Fairchild produced a hybrid having characteristics of both parents. This hybrid was called Fairchild's Sweet William or as Fairchild's mule. This provided a means of artificial hybridization in plants.
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