For twenty years there has been controversy over the level at which Gregor Mendel understood the implications of his experiments for heredity. We argue that he was a hybridist in the tradition of the nineteenth century who (1) designed innovative experiments in plant hybridization and (2) formulated a fundamental new theory for the transmission of traits from parents to offspring based on hypothetical determinants present in germ cells. His own summary, that '...pea hybrids form germinal and pollen cells that in (...) their composition correspond in equal numbers to all the constant forms resulting from the combination of traits united through fertilization', is tantamount to the discovery of what are now called the 'laws' of segregation and independent assortment. Mendel is therefore rightly credited with formulating a new theory of heredity. (shrink)