Dioncea Muscipula, Ellis. 19 



that even in the hand of a steady operator such a stimulus 

 really resolves itself into a series of two or more delicate 

 stimuli applied in succession. 



The leaf of Dioiuea then is truly sensitive throughout its 

 halves to mechanical stimulation, but the capability of receiv- 

 ing sensation impulses is highly concentrated in the hairs. 

 These are so modified for insect catching that the first touch 

 is without visible effect, but prepares the leaf by summation 

 action for a second stimulus which, when applied, causes 

 rapid closure. The advantage of this preparatory warning to 

 the plant is evident, for any adventitious particles blown 

 against it will not cause useless movement. Further, like 

 animal muscle, the contractile tissue of Dioncea must have a 

 mechanical stimulus of a certain strength prolonged through 

 a certain time to effect contraction ; while a prolonged sum- 

 mation series can be applied, the extent of the series varying 

 according to the time interval between each stimulus. These 

 experiments further prove that a minimal contraction stimulus 

 cannot be propagated through the leaf by one touch of a 

 hair, no matter how sharp and powerful the touch is. In 

 other words, the hair mechanism is such in relation to the 

 contractile protoplasm that the latter is not sufficiently 

 altered by one blow, and the minimal amount of alternation 

 necessary for closure can only be obtained after the second 

 stimulus. 



We would here emphasize, however, the considerable diffi- 

 culty one experiences in attempting to place a piece of meat 

 or other solid on either half of a blade without due caution. 

 Very often two or more touches are unconsciously given to 

 the hairs. 



As has been often pointed out, when a leaf is closed by 

 mechanical irritation of the hairs, the halves interlock 

 loosely at first by partial crossing of the marginal bristles, 

 and then slowly firm up till the bristle-bases press against 

 each other. But when an insect or some nitrogenous matter 

 is enclosed, there is a gradual tightening, and the leaf margins 

 recurve, owing to tense pressure of the halves, against 

 a glabrous non-glandular or slightly glandular area that runs 



