Knight was a source for both John Lindley’s scientific theory of horticulture and Davy’s chemistry of agriculture. He essentially outlined the process of evolution by natural selection fifty years before Darwin’s ‘On the Origin of Species’, and his breeding experiments are acknowledged in the first chapter of that work. He had thought about the influence of male and female parents on their offspring and what he called “instinctive hereditary propensity”. Furthermore, although his primary objective was to obtain new and improved varieties of apple, in 1787 he started breeding peas, being an annual plant where results could be more quickly observed than apples. Knight crossed peas of different colours and noted that when the pollen of a purple-flowered plant was introduced into the emasculated blossom of a white coloured one all the resulting peas subsequently gave rise to plants with purple flowers, also observing for the first time how characteristics like height and blossom changed through the generations. His results were published in a Royal Society paper in 1799, establishing traits which were more fully described and statistically analysed into the principles of genetics by Gregor Mendel over sixty years later.
Corresponding with horticulturalists around the world, and sending plants to them, was rewarded with honorary memberships and medals from agricultural and horticultural societies across Europe and America, and in Russia and Australia. He exchanged seeds with a correspondent in Persia and sent large numbers of scions of his new fruit trees to the Massachusetts Agricultural Society, helping to develop the North American apple industry,
Knight had an enquiring mind, a keen sense of observation, and an ability to frame his investigations precisely. Shy and introverted, he worked largely independently in rural Herefordshire for most of his life, but his findings were profound.