2 o4 R-J- fiarvey Gibson. 
they manufacture carbonic acid entirely from their own substance. 
Some succulents growing in ordinary air without carbonic acid emit 
a quantity of oxygen, which exceeds several times the volume of 
the plant. But the gas, which may originally have come from the 
water, is found, on ultimate analysis, to have proceeded only from 
the decomposition of carbonic acid gas which the plants form in 
sunlight from their own tissues. This is proved by the fact that if 
an absorber of carbonic acid be placed near such plants, oxygen is 
no longer added to the surrounding air either by day or night. 
Although their growth may be vigorous, the plants give no indica¬ 
tion of direct decomposition of water. The special peculiarity 
which succulents have of forming carbonic acid from their own 
substance is due, in part, to the feeble porosity of their epidermis 
and in part to the slight contact of their internal tissues with the 
oxygen of the air. There can be no doubt that the major part of 
the hydrogen, which annuals acquire whilst growing freely in air 
and in distilled water is derived from the water which they combine. 
Similarly, in the case of oxygen, for we may conclude both from 
the amount of carbonic acid the plants can decompose in a given 
time, and from the slight alteration which they effect on ordinary 
air, that the amount of oxygen which they imbibe from ordinary air 
is not sufficient to account for the amount they acquire during the 
short period of their development. We must not forget that in the 
decomposition of most dried plants water is the most abundant 
product formed and that oxygen is the chief constituent of it.” 
The chief merit of De Saussure’s work lies in the rigid 
scientific methods he employed in his researches, the logical manner 
in which he marshalled his facts and the careful deductions he 
draws from them. Doubtless his mental attitude owes much to his 
intimate association with his father, the distinguished physicist and 
alpine climber, and perhaps even more to his thorough study of the 
writings of Lavoisier. By many, De Saussure is spoken of as the 
last of the little band of investigators in plant physiology who 
flourished at the end of the 18th and the very early years of the 
19th century. Perhaps it would be more correct to speak of him 
as the forerunner of the new school of chemical biologists represented 
more than a generation later by Boussingault and Liebig. 
If Priestley and Hales were the first to hazard crude suggestions 
of an interesting plot and if Ingenhousz has the merit of blocking 
out, though in the rough, the principal acts in the drama, then De 
Saussure, trained in the school of Lavoisier, may be regarded as the 
