With a busy medical practice to service and so many friends and disparate interests, not to mention his own botanic garden to maintain, Erasmus Darwin's busy life left little time for practical investigations on plants. Through his translation into English of the original Latin texts of Linnaeus, and the precision he had given to botanical language, he had managed however to move botany forward in a very practical way. If he had contributed nothing else to botany, he had helped to bring long needed order to existing knowledge. But it was through his book, Phytologia; or the Philosophy of Agriculture and Gardening, published just two years before his death, that he made his greatest contributions to the progress of botany.

Its significance is twofold. Firstly, it anticipated the mood of the approaching Victorian age for improvement through greater knowledge. The thrust of much of Phytologia is that a better knowledge of plant function can play a key role in improving the growth of crop plants, whether in the garden or the field. There was certainly a desperate need for improvement, for in fourteen of the twenty-three years from 1793 to 1815 there were exceptionally poor harvests in Britain and much of Europe, farmers’ problems being exacerbated from 1804 by the Napoleonic wars that engulfed the continent.

Phytologia is significant secondly, because, with its emphasis on measurement and the practical works of the best investigators of the age, it brought together the latest advances in chemistry and botany. It updated what Erasmus had written in The Loves of Plants, providing a mature synthesis which – even if it contained as much speculation as it did hard fact – proved seminal, being widely quoted by authors and teachers who followed in the next two or three decades. For the modern reader, Phytologia summarizes the state of botany at the start of the nineteenth century. Tellingly, it demonstrates that Erasmus clearly anticipated the emergence from within botany of a separate discipline, the study of function in relation to form.