manner; and I own I had that expectation, when I
first put a sprig of mint into a glass jar, standing inverted in a
vessel of water: but when it had continued growing there for some
months, I found that the air would neither extinguish a candle, nor was
it at all inconvenient to a mouse, which I put into it.

The plant was not affected any otherwise than was the necessary
consequence of its confined situation; for plants growing in several
other kinds of air, were all affected in the very same manner. Every
succession of leaves was more diminished in size than the preceding,
till, at length, they came to be no bigger than the heads of pretty
small pins. The root decayed, and the stalk also, beginning from the
root; and yet the plant continued to grow upwards, drawing its
nourishment through a black and rotten stem. In the third or fourth set
of leaves, long and white hairy filaments grew from the insertion of
each leaf and sometimes from the body of the stem, shooting out as far
as the vessel in which it grew would permit, which, in my experiments,
was about two inches. In this manner a sprig of mint lived, the old
plant decaying, and new ones shooting up in its place, but less and less
continually, all the summer season.

In repeating this experiment, care must be taken to draw away all the
dead leaves from about the plant, lest they should putrefy, and affect
the air. I have found that a fresh cabbage leaf, put under a glass
vessel filled with common air, for the space of one night only, has so
affected the air, that a candle would not burn in it the next morning,
and yet the leaf had not acquired any smell of putrefaction.

Finding that candles would burn very well in air in which plants had
grown a long time, and having had some reason to think, that there was
something attending vegetation, which restored air that had been injured
by respiration, I thought it was possible that the same process might
also restore the air that had been injured by the burning of candles.

Accordingly, on the 17th of August 1771, I put a sprig of mint into a
quantity of air, in which a wax candle had burned out, and found that,
on the 27th of the same month, another candle burned perfectly well in
it. This experiment I repeated, without the least variation in the
event, not less than eight or ten times in the remainder of the summer.

Several times I divided the quantity of air in which the candle had
burned out, into two parts, a