Leaffall and Excretion

A dictionary of biology published as a Penguin book (Abercrombie, Hickman and Johnson, 1951) defines excretion as: “Getting rid of products of metabolism (either by storing them in insoluble form, or by removing them from the body). In animals particularly applies to products of protein metabolism, organs mainly concerned being kidneys of vertebrates, Malphigian tubes of insects, and probably nephridia in many other invertebrates.” The first part of this definition applies as well to plants as to animals; the second part is already an indication that excretion is often especially related to animals. Excretion of plants is generally treated in a stepmotherly way, so summarily in fact that textbooks of botany sometimes not even mention the word. Plants do not show distinct organs of excretion, and their protein metabolism is low compared with the carbohydrate metabolism. The excretion organs of animals which catch the attention, are those eliminating the waste products of the protein metabolism. The waste products of the carbohydrate metabolism in plants, particularly carbondioxide and water, are always treated in the chapter on respiration. The elimination of oxygen is found in the chapter on photosynthesis, but it is not stressed that this is part of the excretion of plants.