Leaves to Traumatic Stimulation . 535 
in the way that we have indicated remain alive, healthy, and 
turgid for a month or more, although all the intercellular 
spaces are thus thrown into uncontrolled communication with 
the external air. The cells that are actually cut through of 
course die and some three layers of adjacent cells may perish 
but never a sufficient number to produce a brown edge visible 
to the naked eye. 
If, on the contrary, a sufficient number of cells be killed to 
produce a visible brown margin to the cut, then the cutting-out 
reaction will follow. All the methods of killing tried, including 
rupturing the cells by a heavy blow, and contact with a hot 
iron, provoke the same reaction. The neatest method that 
we have employed, now to be described, may seem a rather 
indirect one, but we were led to it in the course of our respira- 
tion experiments. If a leaf, cut in any way, be injected with 
water under the air-pump, and if afterwards for a few minutes 
the water be rapidly dried out of it — ns in vacuum — then the 
cells all round the edges of the cuts are disorganized and 
killed and quickly turn brown for a distance of one to three 
millimetres according to the duration of the treatment. The 
brown margin that results is fairly uniform all over any given 
leaf and the cutting-out reaction follows with certainty. 
The first sign of the reaction is visible five or six days after 
the leaves have been put back in a vessel with their stalks in 
water ; at least this holds good for experiments made in April, 
May, and June at laboratory temperatures. This indication 
consists of a fine sharp line running all round the dead region 
at a distance of one to three millimetres. When the leaf is 
viewed against the light, this line is seen to be quite translucent 
and strongly contrasted against the rest of the opaque lamina. 
On cutting sections, at the first glance there appeared to 
be no internal corresponding change, but it was soon seen 
that the spongy parenchyma in the track of the line had 
grown and divided so as to entirely block the intercellular 
spaces and so had produced a local translucency, just like that 
produced by filling up the intercellular spaces of a leaf with 
water. 
