1 6 Macfarlane. — Contributions to the History of 



One hair stimulus followed by a snip stimulus or vice versa 

 acts equally as if two of either had been applied. 



But though at least two stimuli must be communicated 

 through the hairs, and at least two mild forceps stimuli 

 through the lamina to effect closure, a single sharp firm 

 stimulus usually acts similarly. The writer recently experi- 

 mented on twenty-three leaves attached to plants growing 

 wild, and eighteen of these closed after first shock when this 

 was strong. Several of the five that did not close, as well as 

 many of those that received a mild snip-stimulus, showed a 

 peculiarity that had repeatedly been noticed during laboratory 

 experiments. On application of a second stimulus, instead 

 of almost immediate closure, as is ordinarily the case when 

 the hairs are acted on, a latent period of from five to nine 

 seconds elapsed previous to movement, which was then as 

 rapid as usual. It should be noted that the leaf tissue was 

 not ruptured. 



The mechanical action of water was referred to by Darwin 

 as follows : 1 " Drops of water, or a thin broken stream falling 

 from a height on the filaments, did not cause the blades 

 to close ; though these filaments were afterwards proved to 

 be highly sensitive ; no doubt as in the case of Drosera, 

 the plant is indifferent to the heaviest shower of rain." 2 

 " Although drops of water, and of a moderately-strong solu- 

 tion of sugar, falling on the filaments, does not excite them, 

 yet the immersion of a leaf in pure water sometimes caused 

 the lobes to close." We have repeatedly experimented with 

 a thin but sharp jet of water, and the leaves have invariably 

 closed after a short exposure to it. But the behavior of 

 leaves that are suddenly immersed in water, at a temperature 

 like the surrounding atmosphere of from 6o° to 8o° F., is 

 more puzzling as Darwin found. Many observations that the 

 writer has made point to the conclusion that if a leaf attached 

 to a plant is suddenly immersed with the upper surface next 

 the water, no change ensues, but if the process is repeated the 

 leaf closes, i. e., that the two mechanical stimuli, given by the 



1 Insectivorous Plants, p. 2Qt. 

 8 p. 292. 



