Pioneer Investigators of Photosynthesis. 199 
In the “Essay” also Ingenhousz says that plants incessantly 
give out impure air, an indication that at the date of its publication 
he had grasped the fact of the concomitant existence of the two 
processes of photosynthesis and respiration. Indeed, he published 
a paper on the subject in Vienna in 1786, although his statements 
still exhibit some confusion of thought. As Hansen puts it—“ Die 
Assimilation ist entdeckt, sogar Assimilation und Athmung unter- 
scheiden, wenn auch der letztere Vorgang noch nicht begrifflich und 
von der Assimilation getrennt.” 
The years 1770-1790 were fateful years in the history of 
Chemistry and undoubtedly the genius of that period was Lavoisier. 
As Liebig says of him, “ All the facts established by him were the 
necessary consequences of the labours of those who preceded him. 
His merit, his immortal glory consists in this, that he inspired into 
the body of the science a new spirit.” Not the least of his 
services to science was his refutation of the Phlogiston Theory, 
based on exact quantitative analysis, and his skilful employment of 
the balance in experimentation. The extent of Lavoisier’s influence, 
so far as vegetable physiology is concerned, may be readily appre¬ 
ciated by a comparison of the works of Ingenhousz with those of 
De Saussure. 
Another name is prominently put forward by historians as 
contributing largely to the solution of the problem of photo¬ 
synthesis, viz., that of Senebier. Senebier’s claims to distinction in 
this branch of physiological enquiry rest chiefly on three publications 
which, for brevity’s sake, may be termed the “ Memoires,” the 
“ Researches ” and the “ Experiments.” The last-named appeared 
in 1788 and contains the essential points relative to photosynthesis 
published in 1800, in what Sachs terms his “tediously prolix work 
in five volumes the Physiologie Vdgetale.” The first part of the 
“ Experiments ” is devoted to a long controversial attack on 
Ingenhousz, followed by a discussion of what happens to leaves 
exposed under water in darkness, whether they vitiate the air in 
darkness when exposed freely or only when enclosed in glass vessels, 
the effect of heat and moisture on air and of plants in general on 
phlogisticated, dephlogisticated and inflammable air, etc. 
Considerably more than half the volume is given up to decidedly 
“prolix” statements of his views on such subjects and endless 
experiments in support of them, but it must be confessed that these 
statements compare unfavourably with the terse and clear sentences 
of Ingenhousz. The second part deals with the estimation of the 
