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This conclusion is supported by some analogous facts
hereafter to be given.
We will now describe in detail the experiments which were tried. These were
troublesome from our not being able to predict how much cold the leaves of
the several species could endure. Many plants had every leaf killed, both
those which were secured in a horizontal position and those which were
allowed to sleep--that is, to rise up or sink down vertically. Others again
had not a single leaf in the least injured, and these had to be re-exposed
either for a longer time or to a lower temperature.
[Oxalis acetosella.--A very large pot, thickly covered with between 300 and
400 leaves, had been kept all winter in the greenhouse. Seven leaves were
pinned horizontally open, and were exposed on March 16th for 2 h. to a
clear sky, the temperature on the surrounding grass being -4o C. (24o to 25o
F.). Next morning all seven leaves were found quite killed, so were many of
the free ones which had previously gone to sleep, and about 100 of them,
either dead or browned and injured were picked off.


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