Sunbeams, Cucumbers, and Purple Bacteria: the Discovery of Photosynthesis Revisited

SUNBEAMS, CUCUMBERS, AND PURPLE BACTERIA: THE DISCOVERY OF PHOTOSYNTHESIS REVISITED HOWARD GEST* The photosynthetic process ¿s one of the great schemes of nature on which all life depends and one which is not only of the greatest philosophical interest but of immense practical importance, since it is the primary route of energy supply to the living cell and, consequently, the most important source of energy in our technological world.—Sir George Porter [1] In November 1987, Robert Hill, of Cambridge (England) was awarded the Copley Medal of the Royal Society in recognition of his pioneering research on the process of photosynthesis. During the late 1 930s, Hill [2] demonstrated the light-dependent production of oxygen (gas) by chloroplasts, the tiny green bodies present within the cells of plant leaves. These experiments not only localized the actual site of the photosynthetic machinery of plant cells but also proved that water is the source of the oxygen that plants produce. In fact, oxygen production by chloroplasts is a primary source of the Earth's atmospheric oxygen, required for the existence of all animal life. Hill's experiments were a major milestone in more than 200 years of research aimed at explaining the fundamental physiology of plant life. In 1970, Hill wrote an article [3] on "The growth of our knowledge of photosynthesis" from ancient to modern times. After discussing concepts of plant nutrition held by early Greek philosophers, Hill reviews "the beginnings of modern experiment" in the seventeenth and eighteenth centuries, but says little of the brilliant investigations of the Rev. Dr. Stephen Hales (1677-1761). The author thanks Professors R. S. Westfall, H. S. Gordon, P. Wikelund, and F. Brewer for advice and helpful comments during the development of this paper. *Photosynthetic Bacteria Group, Biology Department, and Department of History and Philosophy of Science, Indiana University, Bloomington, Indiana 47405. Copyright is not claimed for this article. 254 I Howard Gest ¦ The Discovery ofPhotosynthesis Stephen Hales After studying divinity at St. Bene'ts College, Cambridge (now Corpus Christi), Hales was ordained and in 1709 became perpetual curate of the parish of Teddington, where he diedJanuary 4, 1761. He proved to be a man for all seasons, mixing parish duties with bold and imaginative scientific experiments. Among the former, Minister Hales was obliged to impose public penances for "immorality" and kept a meticulous parish register; some examples: John RoIt who was murdered in fighting for the May pole: buried May 23, 1710. Twickenham. Hester was Baptised April 15, 1737, being a Foundling dropped at Mr. Everett's Door; her surname is Cradle. James Parsons who had oft eat a shoulder of Mutton and a peck of Hasty Pudding at a Time, which caused his Death, Buried March 27, 1744. Aged 35. Although Hales had no training in medicine, he pioneered in introducing quantitative methods into the study of circulation of the blood. To the dismay of some of his neighbors, he conducted dramatic experiments with horses and other animals to accomplish the first measurements of blood pressure. From his classic book Haemastaticks: In December I caused a mare to be tied down alive on her back; she was 14 hands high, and about 14 years of age, had a fistula on her withers, was neither very lean nor very lusty: having laid open the left crural artery about 3 inches from her belly, I inserted into it a brass pipe whose bore was Ve of an inch in diameter; and to that, by means of another brass pipe which was fitly adapted to it, I fixed a glass tube, of nearly the same diameter, which was 9 feet in length: then untying the ligature on the artery, the blood rose in the tube 8 feet 3 inches perpendicular above the level of the left ventricle of the heart: but it did not attain its full height at once; it rushed up about halfway in an instant, afterwards gradually at each pulse 12, 8, 6, 4, 2, and sometimes 1 inch: when it was at its full height, it would rise and fall at and after each pulse 2, 3, or 4 inches; and sometimes it would fall 12 or 14 inches, and have...