1887.] 



the Protoplasm of certain Plant Cells. 



179 



stimulus of electricity they obey the same laws as animal muscle, and, 

 like certain muscles, may also be relaxed by a feeble tetanising current, 

 go far to suggest that in dealing with the movements of the pul- 

 vinus of Mimosa we have essentially to do with the phenomenon of 

 contractility. 



Although the foregoing results may be said to favour the idea that 

 in irritable organs, movements are brought about by a definite 

 contraction of the protoplasm of the cells of the irritable side, yet the 

 author felt that the matter could only be set at rest by still further 

 strengthening the evidence, and if it were possible, by the actual 

 observation of a cell contracting under the influence of electrical or 

 other stimulation. He therefore turned his attention to the simple 

 filamentous Algae, and among them to an organism which he 

 believed would be peculiarly sensitive to stimulation, viz., Mesocarpus 

 pleurocarpus. The filaments consisting, of rows of cells were first 

 experimented upon, electrically. A single induction shock of 

 moderate strength was found to cause a splitting apart of the 

 previously united transverse walls of the contiguous cells along the 

 middle lamellee. In each cell, the two end walls now project inwards 

 towards the centre of the cell in a concave manner, so that between 

 each pair of cells of the filament there arise a series of double convex 

 lenticular spaces. The rupture does not extend to the free surface. 



With a stronger shock so much contraction is produced that the 

 cells actually fly apart and a complete rupture is effected. The end 

 walls of each cell are now observed to be slightly convex instead of 

 concave. This is a result of the contraction of the freed edges of 

 the external walls, which in consequence of the rupture no longer 

 maintain their cylindrical form. Each cell now resembles a cylinder 

 with its two ends somewhat convex, and its sides very slightly 

 contracted in the immediate neighbourhood of their lines of union 

 with the ends. As in Mimosa the breaking is a stronger stimulus 

 than the making shock. Similar contraction is obtained with ,the 

 tetanising shock and with the constant current. 



Sudden illumination, sudden rise of temperature (45 — 50° C), and 

 the stimulus of certain poisons, bring about the contraction and 

 breaking apart in the most marked manner. Of the poisons, camphor, 

 quinine, strychnine, physostigmine and strong alcohol were found to be 

 exceedingly powerful, with very dilute alcohol no obvious change 

 occurred. The strongest plasmolysing reagents did not bring about 

 the rupture of the cells, but only the partial separation of the end wall, 

 and if the cells are killed by boiling water, by iodine, or by very 

 dilute chromic acid (0*25 per cent.), similar results follow. With 

 1 per cent, osmic acid or 1 per cent, chromic acid the cells may be 

 killed and fixed with little or no contraction. 



The results with plasmolysis entirely agree with those previously 



