322 PROTOPLASM 



automatic movements of the granules in general, was a 

 molecular movement modified by adherence to the proto- 

 plasm. 



Velten (1876) held that it was quite uncertain whether 

 the granules moved actively or passively, and has dealt 

 with this question thoroughly in his memoir " Activ oder 

 Passiv" {CEsterreich. botan. Zeitung, 1876, No. 3). 



Although by reason of my own observations I must rank 

 myself altogether on the side of Nageli's view of the auto- 

 matic movement of the granules, in so far as they are 

 situated on the inner or the outer surface, as the case may 

 be, which limits the protoplasm, I am nevertheless unable 

 to share his opinion concerning the alleged cause of their 

 movement. I incline rather to the belief that the view 

 expressed by Quincke with regard to this cause, so far as it 

 concerns the independent movement of the granules, comes 

 the nearest to the truth. The granules, situated upon the 

 limiting surface of two liquids — a viscid one, the protoplasm, 

 and a more fluid one, the cell sap — move in all probability 

 from the same cause from which pieces of camphor move to 

 and fro continually on the surface of water.^ The cause in 

 question is that the granules continually effect a change in 

 the surface tension at the limiting surface of the two liquids 

 in their vicinity, as a result of which they of course move 

 towards the direction in which the surface tension is 

 heightened. With this change of tension feeble currents on 

 the outermost superficial layer of the two liquids are of 

 course connected, which, however, being very transitory and 

 feeble, only penetrate a small distance inwards, and therefore 

 do not call forth actual streaming movements in the proto- 

 plasm. I am of opinion that the assumption of a universal 

 occurrence of such automatic granular movements would set 

 aside many difficulties which have hitherto been raised in the 

 explanation of protoplasmic movement. The sudden stoppage 

 of these movements, their frequent reversal, the movement of 

 granules on the finest filaments of protoplasm in exactly 

 opposite directions, and finally, the frequent phenomenon of 



■* Compare for these and numerous allied phenomena, van der Mensbrugghe, 

 1869, more especially. 



