1 78 Mr. W. Gardiner. On the Contractility of [Nov. 24, 



nounced inflection which is occasioned by the stimulus of contact or 

 food, by electrical stimulus or, as Darwin has shown, by the stimulus 

 of temperature, oue is led to ask whether these phenomena are not 

 associated with true contractility, and whether the increased impene- 

 trability of the protoplasm of the concave cells is not occasioned by 

 a definite contraction of the primordial utricle and a consequent 

 decrease in the size of the molecular pores. 



Experiments were then made upon the pulvinus of Mimosa pudica. 

 Small pieces of stem (bearing leaves) were cut under a watery solution 

 of eosin, and the pulvini were maintained in a state of stimulation. 

 When the eosin had sufficiently penetrated, transverse and longi- 

 tudinal sections of the pulvinus w T ere made and examined. It was 

 then seen that the dye had readily penetrated into and stained the 

 protoplasm of the outer cells of the convex side of the pulvinus, 

 while on the concave side no staining whatever, of that tract of cellfe 

 situated towards the more external portion, which especially play an 

 active part in movement, had taken place. The more indifferent cells 

 immediately surrounding the vascular bundle also show some contrast 

 in coloration, for in the upper half this tissue remains unstained, 

 while in the lower half some staining occurs. Thus by the process of 

 staining the seat of the especially irritable tissue was clearly brought 

 into view. The author now commenced electrical experiments with 

 the pulvini. Two small pins (which were found not to injure the 

 tissue to any appreciable extent) were inserted into the irritable tissue 

 — one at each end, and fine wires from these pins communicated to 

 the various electrical apparatus as required. When suitably stimulated 

 with either a constant current, an induction shock, or a tetanising 

 shock, the leaf fell immediately contact was made. With the single 

 induction shock the breaking shock was found to be a stronger stimulus 

 than the making. A small piece of stem with the pulvinus attached — 

 the lamina and a portion of the petiole of the leaf having been pre- 

 viously removed — was attached to a lever which wrote upon a revolving 

 drum. On throwing in the electrical stimulus the pulvinus contracted 

 and a curve was obtained. The pulvinus was then turned upside down 

 and, after recovery, w r as again stimulated and a second curve obtained. 

 In both instances the pulvinus raised a weight greater than that of the 

 leaf and leaf stalk. These experiments for the most part only con- 

 firmed those of Cohn and Kabsch, except that they were carried out 

 in further detail ; but one new and important observation was made, 

 viz., that under the influence of a feeble tetanising current the period 

 of recovery of the pulvinus could be materially shortened, and the 

 leaf could be induced to assume tbe position before stimulation in 

 less time than it would have taken under ordinary circumstances. 

 The wonderful delicacy with which the irritable cells of the pulvinus 

 at once reply to stimulation, the fact that in their reaction to the 



