14 PHOTOSYNTHESIS 



to the development of the plant. He noticed, moreover, that in leaves there 

 are small openings, "which," he says, "pour out either air or moisture," 

 though it is quite evident that Malpighi did not recognize the other func- 

 tion of the stomata, namely, the absorption of gases. The existence of 

 stomata was also pointed out by Grew in 1676. 



In considering the attempts which were made at this time to unravel 

 the mystery which surrounds the growth of plants, it becomes manifest 

 that the development of the subject was largely dependent upon that of 

 physics and chemistry. The most confused and contradictory opinions 

 prevailed ujxjn such fundamental questions as the composition of the 

 atmosphere, of water, the nature of combustion, etc. All the more re- 

 markable are the observations of that brilliant investigator, Stephen Hales 

 (1677-1721). On the basis of his extensive experiments he concluded 

 that plants draw some part of their nourishment through their leaves from 

 the atmosphere. He was probably also the first to suggest the influence 

 of light. A contemporary of Newton, Hales regarded light as a substance 

 and asks, "may not light which makes its way into the outer surfaces of 

 leaves and flowers contribute much to the refining of substances in the 

 plant ?" 



To these observations are to be added those of Bonnet who undoubtedly 

 noticed the emission of bubbles of oxygen from a submerged, illuminated 

 leaf (1754). He further established that this emission of gas ceased after 

 dusk. Unfortunately, however, he was unable to follow up his experi- 

 ments or to interpret properly the observations he had made. 



These are very briefly the outstanding observational facts which had 

 been established before the discovery of oxygen. There is no attempt 

 made here to review the early historical development of the subject. Owing 

 to the lack of chemical knowledge the early dissertations now naturally 

 appear exceedingly confused and mingled with much irrelevant matter. 

 i3ut this was all before the discovery of oxygen and the overthrow of the 

 phlogiston theory.^ 



In November of 1773, Pringle. then president of the Royal Society, 

 in presenting Priestley with the gold medal of the society, delivered an 

 address in which he, with great perspicuity, discussed the importance of 

 Priestley's discoveries and their relation to life on the planet in supplying 

 oxygen. This address caused widesjiread comment in the scientific circles 

 of Europe and was destined to exert a great influence on the development 



• For the early history of photosynthesis see : Sachs' History of Botanv Trano 

 lated by H. E. F. Garnesey, Oxford, 1890. Meyer, Ernst H F GeschichteT; 

 Botanik, Koenigsberg 1854 Wiesner. J., Jan Ingen-Housz, Vienna, 1905 Hansen 

 A., Geschichte der Assnnilation und Chlorophvllfunction, Leipzig 1882 Gihsnn 

 R. J. H.. Pioneer Investigators in Photosynthesis. New Phytolo<^ist 13 191 20^' 

 (1J14). Kimpflm, G.. Essai sur L'assimilation Photochlorophylliaine dn' rprhr^m 

 Lyon 1908. Wittwer, W. C, Geschichtlichc Darstellung der verSdenen Lehren 

 uber die Respiration der Pflanzen. Mimchen, 1850. For accounts of van Helmont's 

 hfe and work: Kopp. H., Geschichte der Chemie. 1843, I, p 117 Mevlv 

 f891 p 7Z'°"' ^ "'''"""^ °^ Chemistry. Translated by G. McGowan London 



