THE CLOSING RESPONSE IN DIONAEA' 
WILLIAM H. BROWN AND LESTER W. SHARP 
(WITH ONE FIGURE) 
Despite the attention attracted during the past century by the 
extraordinary reactions of Dionaea muscipula Ellis, there remains 
much uncertainty with regard to many points in its behavior. This 
uncertainty has led the present writers to carry out the work here 
reported. 
The structure of the leaf is so well known that its description here 
is unnecessary. It may be well, however, to recall the fact that the 
leaf blade consists of two valves, each of which bears upon its upper 
surface three short, rather stiff bristles. Mechanical contact with 
these bristles causes the two valves to close together upon each other. 
Relation of intensity to number of stimuli 
Darwin (3), SACHS (9), BATALIN (1), DETMER (4), MuNK (7), 
and others held that one contact stimulus was sufficient to produce 
the closing response. Darwin (3) and BuRDON-SANDERSON (2) 
showed that an extremely slight stimulus might be inadequate, while 
MACFARLANE (6) concluded from his researches that under ordinary 
conditions two mechanical stimuli are always necessary. In inves- 
tigating this question it is of course necessary to avoid all possibility 
of shaking, which might cause uncertainty as to the number of 
stimuli applied. In the present experiments a stiff straw was 5° 
supported that it could be adjusted to any desired position and 
moved mechanically by means of a rack and pinion and milled head. 
By this method the movement of the straw could be accurately con- 
trolled, and the number of stimuli definitely known. 
Leaves of plants which had been kept at 15° C. for one to pee 
hours were stimulated by pressure upon one of the sensitive hairs, 
and it was found that closure almost never resulted after one such 
stimulus, even though the hair was bent down so as to touch the 
t Contribution from the Botanical Laboratory of the Johns Hopkins University, 
No. 12. 
Botanical Gazette, vol. 49] [age 
