364 LIGHT AND THE BEHAVIOR OF ORGANISMS 



certain chemical changes which are produced by the blue. 

 In Daphnia the maximum is in the yellow and green, and 

 in many of the plants it is in the violet. These reactions, 

 too, are associated with chemical changes, but since these 

 chemical changes are caused by rays differing in wave 

 length from those which are most efficient in Amoeba, the 

 chemical compounds must also be different unless the dif- 

 ference in the effect of the different rays can be accounted 

 for by assuming the presence of certain inactive substances 

 which influence the chemical reaction, or by assuming 

 selective absorption on the part of the organism. It is 

 however not likely that the difference in reaction to differ- 

 ent rays can be explained thus. We may then conclude 

 that the chemical changes associated with reactions are 

 not the same in all organisms. While we do not at present 

 know what these changes are, there are prospects that 

 future investigations along this line may demonstrate the 

 nature of some of them at least, especially after the photo- 

 chemical reactions in organic and inorganic substances have 

 been more thoroughly investigated. 



(8) In plants and the lower organisms on which the 

 relative stimulating efficiency of the different rays is fairly 

 constant the chemical changes accompanying the reactions 

 may be relatively simple, but in the higher forms in which 

 the relative stimulating efficiency of the different rays 

 varies it seems evident that the chemical changes must be 

 very complicated. If this is true, it contradicts Loeb's 

 general conclusion that- the reaction mechanism associated 

 with photic responses in plants is the same as that in 

 animals, that " the dependence of animal movements on 

 light is in every point the same as the dependence of plant 

 movements on the same source of stimulation " (1905, 

 p. 81). 



(9) Honey bees, some fishes, birds and mammals, and 

 probably some of the decapod Crustacea and spiders, can 

 unquestionably, and many of the lower forms with well- 

 developed eyes can probably, distinguish the different 



