SPECTRAL COLOR AND STIMULATION 497 



however, not fully in harmony with the limits of this field as 

 given above, which according to my calculations indicates that 

 it lies between 494.7 and 451.5 mm- 



The aggregation of the euglenae under the conditions of the 

 experiments was undoubtedly dependent upon shock reactions, 

 for Engelmann says (p. 398): ''Hier, zwischen den Wellen- 

 langen 0.47 and 0.49 fx, fahren sie fort, sich in normaler Weise 

 zu bewegen, kehren aber immer an der Grenze von Dunkel, von 

 Griin, die meisten auch an der Grenze von Indigo oder Violett 

 wdeder um." Engelmann maintains moreover (p. 399) that by 

 means of a microspectral objective he was able to ascertain the 

 sensitivity of Euglena to changes of intensity in different regions 

 of the spectmm and that he found "dass der kleinste fiir Eu- 

 glena merkbare Intensitiitsunterschied fiir Roth, Gelb, und 

 Grtin ansehnUch grosser ist als fiir Blau (zwischen 0.47 und 0.49 

 fx Wellenlange) und auch fiir Violett. 



The results obtained by Engelmann regarding the location of 

 the region of maximum stimulating effect in the prismatic spec- 

 trum are in close agreement with those obtained by the writer 

 and presented in the preceding pages. In the experiments of the 

 former, however, the results depended upon shock-reactions (time 

 rate of change of intensity) and in the latter upon orientation. 



If the contention of Loeb and Wasteneys ('16, p. 235) is cor- 

 rect, that the photochemical substances in all organisms having 

 the regions of maximum sensitiveness in the same location in the 

 spectrum belong to the same type, then the photochemical sub- 

 stances associated with shock-reactions and those associated with 

 orientation must belong to the same type. And if this is true it 

 lends strong support to the contention of the writer and others 

 that shock-reactions and orientation in Euglena are fundamen- 

 tally the same, in fact, that orientation is the result of shock- 

 reactions; and it militates against the contention of Loeb ('06), 

 Bancroft ('13) and Torrey ('13) that these phenomena are fun- 

 damentally distinct. 



Euglena gracilis 



Euglena gracilis was found in great abundance in a small tem- 

 porary clay pool at Nela Park, August 5 in the morning. Some 



