70 
Blackman and Paine.—Studies in the 
with these changes in permeability. Owing perhaps to the observations 
and conclusions of Lepeschkin with reference to nyctinastic movements 
the view seems to have gained ground, in spite of the inherent objection 
already cited, that a similar change of permeability will explain the response 
of Mimosa to shock. 
It seemed of importance that this view should, if possible, be subjected 
to the test of experiment. A method to be suitable must be one by which 
the exosmosis of very small quantities of the cell-contents can be recognized, 
for it would be difficult to work with more than a single pulvinus. As 
the increase of permeability, if it occurs, would almost certainly lead to the 
increase of rate of exosmosis of electrolytes as well as of non-electrolytes , it 
seemed likely that the electrical conductivity method for the estimation 
of dilute solution of electrolytes could be used to solve this question. 
Experiments using this method were begun some years ago ; since 
that time the method has been used in many investigations on cell 
permeability. The erratic behaviour of the pulvini, i. e. the refusal of 
many of them to respond, after removal from the plant, to shock stimuli, 
has delayed the work. 
Experimental. 
The method employed was essentially the same throughout; a pulvinus 
of Mimosa pudica was removed from the plant and immersed in a small 
volume of ‘ conductivity water ’ distilled over glass. The rate of exosmosis 
of electrolytes was determined periodically by the electrical conductivity 
method. 
After removal of the leaf from the plant by a clean cut at the base of 
the pulvinus the upper part of the petiole was cut away so that a length of 
about an inch and a half remained attached to the pulvinus. In order to 
increase the rate of diffusion the internal tissue was further exposed by 
slicing away an equal portion of tissue from each side of the pulvinus, but 
leaving the upper and lower surfaces in the main intact. This operation 
was made with a sharp scalpel and as speedily as possible. The pulvinus 
was immediately placed in water so as to wash away the contents of the 
cut cells before beginning the experiment. The petiole was then gripped 
by a split rubber cork held in a cork-borer, which was lowered by a rack 
and pinion until the pulvinus was completely immersed in the liquid of the 
conductivity ‘ cell ’. Treatment of the pulvinus in this way did not destroy 
its power to contract when stimulated. In a great many cases response to 
stimulation was obtained within fifteen minutes from the time of removal 
of the pulvinus from the plant; in others a period of some thirty or thirty- 
five minutes elapsed before the pulvini becomes stimulable. The unstimu- 
lable condition seemed to be associated with extreme turgor of the cells 
of the under side of the pulvinus, since it was frequently observed that the 
