54 
branch of the subject is afforded by the experiments of 
M. de Saussure. He observes, that a small portion 
of oxygen gas exists in the earth, and he was desi- 
rous to know whether the contact of this gas with 
the roots of plants was useful to vegetation. He 
therefore took several tubulated recipients, and, fill- 
ing them with distilled water, set them to stand in 
separate basons of mercury. Having then drawn 
some young chesnut trees out of the earth, he put 
the roots of one tree through the mouth of each 
vessel, so that they should be entirely in the vessel, 
while the leaves were in the open air ; the mouth of 
each vessel was then carefully closed by a lute ap- 
plied to the stem of the plant. Through the bottom of 
each recipient, a given quantity of gas was next in- 
troduced, which caused the water to fall, until the 
extremities only of the roots were immersed in it, 
while their greater part was exposed to the imme- 
diate contact of the gas employed. 
277. In this manner he exposed the roots to ni- 
trogen, hydrogen, and carbonic acid gases, and like- 
wise to atmospheric air. The plants, whose roots 
were in contact with carbonic acid gas, died a- 
bout the seventh or eighth day ; those which 
had their roots exposed to nitrogen and hydrogen 
gases died at the same time, which was about the 
thirteenth or fourteenth day : while three separate 
plants, whose roots vegetated in contact with atmos- 
pheric air, were still vigorous at the expiration of 
three weeks, when an end was put to the experiment. 
He adds, that the nitrogen and hydrogen gases suf- 
fered no change, but the bulk of air was increased by 
