7 1 
Permeability of the Pulvinus of Mimosa pudic'a . 
contour of this side during the dormant period was convex, but when it 
returned to the normal, slightly concave condition the response to stimuli 
was again established. As already stated, for some reason unexplained 
some pulvini never recovered from this dormant condition. In one case, 
however, a pulvinus, which during two hours had given no response to 
stimulation, was left immersed in the cell at 4 p.m., and was found two 
hours later to have recovered. The factors which determine this behaviour 
were not discovered, and a certain element of doubt always existed as to 
whether a given pulvinus would behave normally. Such cases of failure 
to obtain response to stimulation were in the later part of the work reduced 
to one in ten. 
The conductivity cell employed was designed for the purpose, and is 
specially serviceable for conductivity determinations where the volume of 
liquid available is very small. The actual cell A (Fig. 1) was a small glass 
cup six or seven millimetres in diameter with electrodes, two millimetres 
apart, fused in at the sides; the electrodes had an area of about two square 
