412 FRANK W. BANCROFT 



SO this mechanism cannot depend upon shock-movements which 

 are the responses to temporal change of intensity. There re- 

 mains then only the mechanism for direct heliotropic orientation 

 which is capable of explaining these phenomena. 



H. Galvanotropism and heliotropism 



Hitherto no one, so far as I know, has succeeded in demon- 

 strating galvanotropism in Euglena, I also failed to get certain 

 galvanotropism in many cultures but obtained good galvanotro- 

 pism in others. Euglenae from Culture A gave a weak temporary 

 anodal galvanotropism lasting only from three to twelve minutes, 

 but only when the individuals were taken from dense gatherings. 

 The scattered individuals gave nothing. Good permanent catho- 

 dal galvanotropism was obtained from the following cultures: 



1. Hay infusion in -g^'o citric acid, ten days old. 



2. Pea decoction in y^ o citric acid, nineteen days old. 



3. Pea decoction in 5*^^ citric acid, thirty-five days old. 



Good permanent anodal galvanotropism was also obtained with 

 individuals from (2) and (3) which were examined in chondrus 

 (Irish moss) jelly and tap water respectively. But no attempt 

 was made to work out the conditions responsible for cathodal and 

 anodal galvanotropism. 



When these strongly cathodal Euglenae were first subjected to 

 the current their response to the reversal of the current was more 

 rapid and accurate than any heliotropism which I have seen. But 

 as the experiment continued the rapidity of reversal became pro- 

 gressively less and less until soon they turned in sweeping curves 

 just as Euglena becomes oriented to light of medium intensity. 

 Later the galvanotropism became still weaker, individuals could 

 no longer be seen to reverse when the current was reversed and it 

 was only by watching for some time that it could be seen that 

 most of the plants had turned towards the new cathode. 



Cathodal individuals that were orienting in sweeping curves 

 were examined in chondrus jelly under a 4 mm. Zeiss objective. 

 Under these conditions the flagellae and all the details of the ori- 

 enting reaction could be most distinctly seen. Euglenae moving 



