320 PROTOPLASM 



idea that the granules possess no power of movement of 

 their own, but are only carried about by the streaming 

 movements of the protoplasm, upon or in which they are 

 lodged. Berthold also represents this view, which has been 

 current since M. Schultze. 



When I was following out the phenomena of movement 

 exhibited by these granules, as they can be plainly observed 

 in plant cells {Tradescantia hairs, for example), I was 

 involuntarily forced to the idea that their movements could 

 not be in any way passive, in the sense that they were 

 simply carried along by the streams of protoplasm as sus- 

 pended corpuscles, but that they must, in a certain sense, 

 be of an active nature, i.e. that the cause of movement 

 must reside near or within the granules themselves. 

 Although this idea was always aroused, as has been 

 remarked, by the consideration of vegetable cells and 

 Sarcodina, I could not come to any decision upon this 

 question in objects of this kind, which at the same time 

 exhibited lively protoplasmic movements. Only by the 

 study of a peculiarly favourable object, which recently came 

 into my hands, was a sure proof at last obtained that such 

 an automatic movement of the granules must, as a matter of 

 fact, take place. This object is a large diatom of the genus 

 Surirella. At the limiting surface of its protoplasm turned 

 towards the cell sap there are numerous granules in a state 

 of incessant movement to and fro in the most various 

 directions, which have already been mentioned before as 

 chromatin-like granules (p. 91). It seems a point of very 

 special, interest that these motile protoplasmic granules 

 are only to be met with in this organism at the surface 

 of the protoplasm by which the latter is limited towards 

 the cell sap, while I was not successful in finding corre- 

 sponding granules in the interior of the protoplasm. It is 

 also shown beyond a doubt, by tracing their movements 

 more accurately, that they glide along the limiting surface 

 of the protoplasm, and partly, at any rate, project from the 

 protoplasm into the cell sap. Now since, as I have already 

 briefly described in another place (1891), the protoplasm of 

 this diatom is itself in a state of relative quiescence, as can 



