Pioneer Investigators of Photosynthesis. 195 
composition of the air had been determined and until the establish¬ 
ment of the New Chemistry. In 1754 Black discovered “fixed 
air,” rechristened “carbonic acid” by Lavoisier in 1781. In 1774 
Priestly discovered “ dephlogisticated air,” a discovery which he 
communicated, a few weeks after he had made it, to Lavoisier who 
in 1782 renamed Priestley’s gas “oxygen.” With Lavoisier’s 
further identification of a residual “ non-vital air,” “ azote ” or 
nitrogen, and his analysis of water into hydrogen and oxygen, the 
way was opened for the two physiologists whose names stand out 
pre-eminent at the close of the 18th and the dawn of the 19th 
century—Ingenhousz and De Saussure. 
In discussing the work of the founders of Plant Physiology, 
Sachs is curiously contemptuous of the part played by Priestley— 
a not uncommon failing of this distinguished botanist when 
criticising the work of English investigators. “ The establishment 
of the fact,” says Sachs, “that parts of plants give off oxygen under 
certain circumstances did little or nothing to forward the theory 
of their nutrition; and that was all that vegetable physiology owes 
to Priestley.” It is consoling to find that Sachs dates “ the 
revolution which was effected in chemistry between 1770 and 1780” 
from the “discovery of oxygen gas by Priestley in 1774.” The 
discovery of the gas itself and the part that discovery played in 
the New Chemistry founded by Lavoisier, not to mention Priestley’s 
observations on the exhalation of oxygen from green parts of plants 
in sunlight, surely entitle him to a somewhat more appreciative 
recognition. A comparison of Priestley’s writings and Sachs’s 
comments upon them raises the suspicion that the latter either 
failed to comprehend Priestley’s somewhat old-fashioned English 
or that he contented himself with an inaccurate summary written 
for him by one of his pupils. Ingenhousz, in the preface to his 
“ Experiments upon Vegetables,” expresses a very different opinion 
of the value of Priestley’s work. “ The discovery of Dr. Priestley 
that plants thrive better in foul air than in common and in 
dephlogisticated air, and that plants have a power of correcting bad 
air, has thrown a new and important light upon the arrangements 
of this world. It shews, even to a demonstration.that the 
air, spoiled and rendered noxious to animals by their breathing in 
it, serves to plants as a kind of nourishment.” 
Sachs also says:—“ After Priestley had ceased his experi¬ 
ments on plants in 1778”—this is a perfectly gratuitous assumption 
on Sachs’s part—“ he observed that there was a deposit of matter 
