18 DISCOVERY OF PHOTOSYNTHESIS CHAP. 2 



of llie Royal Society, John Piingle, made on the occasion of the presenta- 

 tion of tiic Cople.y medal to Priestley in 177;i In this speech, Pringle 

 extolled the importance of Priestley's disco\'ery, which showed that the 

 apparently useless or even poisonous plants "do not grow in vain," and 

 that "salutary gales convey to the woods that flourish in the most remote 

 and unpeopled regions, our vitiated air, for our relief, and for their 

 nourishment." 



However, Ingen-Housz' plans for studying this mutual well-being of 

 animals and plants, even if the.y were actually conceived in 1773, did not 

 mature for seven years, and thus not until after the publication of 

 Priestley's observations on the "green matter" which evolved purified 

 air in sunlight. Ingen-Housz — the passenger — was spending the year, 

 1779, in England on a leave of absence from Vienna. In June of this 

 year he retired to a "small villa" in the Enghsh countryside, and there, 

 working "from morning till night," he performed, in less than three 

 months, more than five hundred experiments. With amazing speed, the 

 results of these experiments were ready for presentation to the public in 

 October of the same year, in the form of a book entitled Experiments 

 upon Vegetables, discovering Their Great Power of Purifying the Common 

 Air in Sunshine and Injuring it in the Shade and at Night. The book was 

 dedicated to John Pringle, whose presidential address seven years earlier 

 had first aroused Ingen-Housz' interest in plant chemistry. Ingen-Housz 

 explained the hurried publication by the necessity of returning to Vienna; 

 but he also realized the importance of his discoverj'^ and was decided not 

 to let anybody deprive him of it or even as much as share in it. 



The progress achieved by Ingen-Housz in these three months was 

 indeed remarkable. Despite numerous errors which can be found in his 

 book and which were caused partly by haste and partly by the ready 

 belief of the author in his conjectures (so different from the conscientious- 

 ness of a Priestley), Ingen-Housz has clearly established in this book the 

 fundamental facts of photosynthesis. He wrote: 



"I observed that plants not only have a faculty to correct bad air in six or ten days, 

 by growing in it, as the experiments of Dr. Priestley indicate, but that they perform this 

 important office in a complete manner in a few hours; that this wonderful operation is 

 by no means owing to the vegetation of the plant, but to the influence of the light of 

 the sun upon the plant. I found that plants have, moreover, the most surprizing faculty 

 of elaborating the air which they contain, and undoubtedly absorb continually from the 

 common atmosphere, into real and fine dephlogisticated air; that they pour down con- 

 tinually a shower of this depurated air, which . . . contributes to render the atmosphere 

 more fit for animal life; that this operation . . . begins only after the sun has for some 

 time made his appearance above the horizon . . .; that this operation of the plants is 

 more or less brisk in proportion to the clearness of the day and the exposition of the 

 plants; that plants shaded by high buildings, or growing under a dark shade of other 

 plants, do not perform this office, but, on the contrary, throw out an air hurtful to 

 animals; . . . that this operation of plants diminishes towards the close of the day, and 



