1910] BROWN & SHARP—CLOSING RESPONSE IN DIONAEA 295 
production of some chemical substance as the result of excitation; 
that the amount of this effect varies with the intensity of the stimulus; 
and that the amount of stimulation necessary for closure varies with 
different leaves, probably with different conditions of the plant. 
Localization of perception 
Darwin (3) held that the surface of the blade is very slightly, and 
the footstalk not at all sensitive. MAacFARLANE (6) showed that 
scraping the surface or squeezing the blade with steel forceps would 
cause closure, and concluded that “the leaf of Dionaea, then, is truly 
sensitive throughout its halves to mechanical stimulation, but the 
capacity for receiving sensation impulses is highly concentrated in 
e hairs.” This writer states, however, that two pinches with the 
forceps are required to cause closure. In our experiments, leaves 
responded to one, two, or even more such pinches, according to the 
Strength of the stimulus and the condition of the leaf. It thus 
appears that MACFARLANE’S conclusion is supported, in that all parts 
of the leaf are sensitive, and the question is raised whether the pro- 
toplasm of all parts may not be equally sensitive to stimulation, and 
that the hair functions simply as a mechanism which compresses 
certain cells. OvupeMmANs (8) and BATALIN (I) came to the con- 
clusion that the base of the hair is the sensitive region, while HaBER- 
LANDT (5) has pointed out near the base of the hair a layer of cells 
which appear especially fitted for being bent, and thus having their 
contents compressed. The latter author considered this layer the 
Sensitive region, and expressed surprise that the rest of the leaf 
should be sensitive at all. 
When a hair is stimulated by contact, it is first bent laterally and 
downward, held in this deformed position for a short time, and then 
allowed to spring back to its original position. If stimulation be due 
to a compression of cells at the base of the hair, the downward move- 
ment alone should cause closure. To test this, a stiff straw was 
Supported as in former experiments, so that it could be accurately 
adjusted and held definitely in any position. Two downward 
thrusts on the same sensitive hair without an intervening release 
caused in every case at 15° complete closure. With a temperature 
