ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 457 



In both cases transpiration is a function of living colourless proto- 

 plasm, this function, however, being greatly enhanced by the presence 

 of chlorophyll. 



The author made a number of experiments on transpiration in a 

 saturated atmosphere, selecting Buxus sempervirens, Ligustrum vulgare, 

 and Epilobium hirsutum, to represent three types of foliage. The result 

 obtained was that, as long as the plants were exposed to diffused day- 

 light they continued to lose weight, although the atmosphere was appa- 

 rently perfectly saturated all the time. 



Finally, the author gives the details of some experiments on evapora- 

 tion in a saturated atmosphere. The results which he obtained prove 

 that dead saturated substances continue to evaporate, notwithstanding 

 that the atmosphere in which they are suspended is apparently saturated. 



(3) Irritability- 

 Contractility of the Protoplasm of Certain Cells.* — Mr. W. Gardiner 



describes certain experiments made upon the pulviuus of Mimosa pudica. 

 Transverse and longitudinal sections were cut under an aqueous solution 

 of eosin, and it was found that the dye readily penetrated into and 

 stained the protoplasm of the outer cells of the convex side of the pul- 

 viuus ; the tract of cells situated towards the more external portion, the 

 seat of the specially irritable tissue, was left unstained. Electrical 

 experiments with the pulvini were then made. The wonderful delicacy 

 with which the irritable cells of the pulvinus at once reply to stimula- 

 tion suggest that in dealing with the movements of the pulvinus of 

 Mimosa we have essentially to do with the phenomenon of contractility. 

 Experiments were then made with an organism peculiarly sensitive to 

 stimulation, viz. Mesoca'rpus pleurocarpus. 



The author states in conclusion that there can be no doubt that the 

 protoplasm of plant-cells, like that of animal-cells, is capable of active 

 contraction, and he believes that in all irritable organs the movements 

 are brought about in consequence of a definite contraction of the proto- 

 plasm of the irritable cells, and that during such contraction some of 

 the cell-sap escapes to the exterior. 



Movement of Leaf of Mimosa pudica.f — Dr. S. H. Vines has at- 

 tempted to get some further information as to the nature of the mechanism 

 of the movements of the leaf of Mimosa pudica. Experiments with 

 atropin on the main pulvinus resulted in showing that movement of the 

 petiole on stimulation becomes gradually less and less, until it ceases 

 altogether, the petiole retaining the more or less nearly horizontal 

 diurnal position ; with the leaflets the induced movement is at first well 

 marked, and they readily recover the expanded position ; but gradually 

 they failed to expand completely after stimulation, and at last remain 

 completely closed. With physostigmin the effect on the main pulvinus 

 is gradually to diminish the extent of recovery after stimulation, until 

 eventually the pulvinus retains the position characteristic of stimulation ; 

 the closing movement of the leaflets becomes less and less marked, until 

 finally they make no movement at all, but remain open. 



The effect of atropin, then, is that of darkness, while that of physo- 

 stigmin is that of light. 



* Proc. Roy. Soc, xliii. (1887) pp. 177-81. 



t Ken. Brit. Absoo. Adv. Sci., 1887 (1888) pp. 742-3. 



