292 PROTOPLASM 



and protoplasm, which produce the streaming movements 

 in the plant cell. In this point I think Berthold has hit 

 the mark ; on the other hand, I cannot consider as satisfac- 

 torily grounded his efforts to explain, by means of these pro- 

 cesses, isolated cases of movement in vegetable protoplasm. 

 The very important case of the so-called rotation of the 

 protoplasm in a constant direction remains, in my 

 opinion, unexplained. For the remarks that Berthold makes 

 upon this point on p. 118 can scarcely be considered as 

 a sufficient explanation. He thinks that the rotational 

 streaming has gradually arisen from numerous irregular 

 streamings, such as occur in the so-called circulation, in 

 the following way. " The stronger currents will gradually 

 suppress the weaker, ,and draw them along in their 

 direction, and thus in the struggle for existence (!) only a 

 single rotational current will be left remaining among them, 

 for only in this way would the principle of least resistance 

 be satisfied." Berthold further supposes that a special 

 increase of the fluidity of the protoplasm is a condition 

 for the development of the siinple rotatory current. An 

 explanation such as the above can hardly be considered 

 a physical one, although Berthold means to give one of this 

 kind, for such principles as the " struggle for existence " are 

 here quite inadmissible and do not explain anything. A 

 system of numerous streams will always remain as such 

 when the causes persist which produce them ; if no change 

 takes place in the causes, a single stream cannot possibly 

 be formed. With regard also to the principle of least 

 resistance I am very sceptical, since I freely confess that 

 I do not quite understand what Berthold really pictures 

 to himself by it. In order to explain rotation currents 

 on the ground of Berthold's hypothesis, which, as I have 

 said, I regard as the only correct one, even after all the 

 observations of my own which are detailed in this book, it 

 is necessary to show why, when, and in what way there 

 arises a single powerful current of this kind, which, as we 

 have already been convinced by the streamings in the foam- 

 drops, can suppress feeble local streams with perfect ease by 

 gradually removing the cause of their origin ; and we must 



