H62 Mast, Orientation in Euglena with some Remarks on Tropisms. 



a fairly definite meaning? Thus in place of tropism we would have 

 orientation or reaction, in place of positive or negative phototropism, 

 geotropism, etc., we might use positive or negative orientation or 

 reaction to light, gravity, etc. ; and in place of positively or nega- 

 tively phototropic, geotropic, etc., we might use photo-, geo-, nega- 

 tive or positive, etc., or merely negative or positive reaction to 

 light, gravity, etc. These terms are purely descriptive, and there 

 could be no confusion as to their meaning. Thus the controversy 

 regarding the definition of "tropisms" would end and attention 

 would be focussed on the various processes involved in orientation 

 and reactions. 



The desirability of this is made strikingly evident by the con- 

 tents of a recent paper by Ewald (1913) referred to above. In 

 this article Ewald, like Bancroft, throws to the wind most of 

 Loeb's ideas regarding "tropisms''. He says (p. 583), ,,Es ist ein 

 Irrtum, wenn von verschiedenen Autoren die Tropismentheorie 

 selbst mit den angefiihrten Argumenten Loeb's identifiziert wird." 

 And, like Bancroft, he defines tropisms (p. 584) as compulsory 

 orientation: ,,Tropismus ist (ohne Riicksicht auf den Mechanismus 

 der Reaktion), der Ausdruck fur eine zwangsweise Richtungsbewegung 

 in bezug auf eine Energiequelle." He closes the article with the 

 following startling statement (p. 597): ,,Nachdem kurzlich Ban- 

 croft auch die von Jennings und Mast auf Grund ihrer Ver- 

 suche an Euglena erhobenen Einwande gegen die Tropismenlehre 

 durch exaktere Experimente widerlegt hat, diirfte die Bahn nun- 

 mehr wieder auf einige Zeit fur die rein experimentelle Arbeit 

 frei sein." 



Thus it is evident that Ewald holds that orientation due to 

 a series of shock-reactions as described by us for Euglena opposes 

 his tropism theory (compulsory orientation) for all that we have 

 shown is that orientation in Euglena is due, at least at times, to 

 shock-reactions. Bancroft, however holds that they are in full 

 harmony with this theory. He says (p. 385), "Does Euglena become 

 oriented to light as directly as its method of orientation admits; 

 or does it orient indirectly, by the method of trial and error? In 

 either case the reaction will be heliotropic, but the method 

 of orientation will be different?" (Italics are mine). 



If these two investigators, closely associated in the same labora- 

 tory as they were, differ so radically in the interpretation of their 

 own definition of the term tropisms, what might be expected of 

 others? Could anyone desire a more striking illustration of the 

 futility of attempting under present conditions to convey by the 

 use of this term, anything but the vaguest sort of an idea. 



It may be said, however, if Ewald means by compulsory 

 orientation merely that there are no psychic phenomena involved in 



