TABLE OF CONTENTS I have discovered what I have long been in quest of, viz, the process in nature by which air rendered noxious by breathing, is restored to its former salubrious condition.
Joseph Priestley, letter to Philus Lindsey, August 1771.
Green plants, and therefore ultimately all other higher forms of life, depend on organic carbon derived from carbon dioxide in processes driven by light energy. Central to every aspect of such photosynthetic carbon assimilation by leaves lies the Calvin cycle. In this cyclic sequence of reactions, carbon dioxide is added to an acceptor molecule. The newly formed addition compound then undergoes a series of changes, including reduction, so that a stable product is formed and set aside. At the same time, the CO 2-acceptor is regenerated and new molecules of acceptor formed so that the process may continue and the green plant may grow.
Remarkably, there is a still a popular belief, reinforced by gardeners who habitually talk about feeding their plants, that green plants obtain most of their nutriment from the soil. In fact, the fallacy of this supposition was demonstrated as long ago as the seventeenth century by van Helmont, who grew a willow in a tub of weighed soil. After watering for five years, the willow weighed 164 lbs, more...
