Dioncea Muscipula, Ellis. 17 



water, act like the two shocks communicated through the 

 hairs or by forceps snip or otherwise. But while this is indi- 

 cated by twenty-one out of twenty-nine leaves, it must still 

 be emphasized — as showing the need for continued experi- 

 ment — that leaves have repeatedly closed on first immersion 

 in water at, or very near, the same temperature as the sur- 

 rounding air. Still more puzzling is the effect of gradual 

 immersion in water. Round Wilmington, N. C, the writer 

 dug up thirteen plants in succession, each surrounded by large 

 balls of soil. He carefully and slowly immersed these, in 

 natural position, underwater. Every leaf closed on all of the 

 plants, with the exception of two which did so when the 

 plants were gently removed from the water. This behavior 

 led him to attempt to localize the centre of movement more 

 exactly. Selecting twelve fine leaves, and holding them by 

 the petiole, he slowly immersed these from the tip of the 

 blade inwards, and invariably when the water reached the 

 level of the first pair of opposite hairs rapid closure followed 

 Some of these were repeatedly withdrawn when the water had 

 reached to about one-third of a line or more from the hairs, 

 but no change followed. Seventeen leaves were then gradu- 

 ally immersed obliquely, in a vessel, so that the water would 

 first touch a single hair. Every leaf closed when the water 

 wetted the hair. We thus learn that while rain drops or a 

 slight water current falling on the upper leaf surface is with- 

 out effect, a sharp water impact, or immersion so as to cover 

 one or more hairs, starts contraction. But while water impact 

 is purely mechanical, a totally different explanation is needed 

 in the latter case. We know from Sanderson's electrical 

 researches that the upper leaf surface is positive to the under, 

 and that the hair region is specially sensitive in its electrical 

 condition, so that when the leaf was immersed, the water 

 might act as a conductor for the electricity between the upper 

 and lower surfaces. That liquids act differently was proved 

 by immersing in olive oil, for then no change occurred even 

 after repeated dipping. The leaf, however, was still sensitive, 

 for when irritated after two minutes it closed. Petroleum oil, 

 however, set up rapid movement. At the present stage we 



