HELIOTROPIC REACTIONS ANIMALS AND PLANTS 221 



tropisms from the same general viewpoint. What sensations are 

 aroused in a Paramaecium which is forced to swim to the cathode 

 under the influence of the galvanic current, or in a Palaemonetes 

 which is forced to swim or walk to the anode? 



Since Hess starts with an arbitrary assumption, namely that 

 the hehotropism of lower animals is due to their sensations of 

 brightness and that they are totally color blind, it is not unex- 

 pected to see him come into conflict with facts in more than one 

 direction, v. Frisch' has shown by experiments which appear 

 to us conclusive that bees (which are also positively heliotropic 

 and which according to Hess are totally color blind) can be trained 

 to go to yellow or blue cardboards distributed among similar 

 cardboards of different shades of gray; while they can not be 

 trained to go to definite shades of gray under similar conditions. 

 Even in Daphnia v. Frisch and Kupelwieser,^ and Ewald^ 

 have been able to demonstrate selective effects of wave lengths 

 different from those found in the totally color blind human. 



A second conflict between Hess's view and reality is due to the 

 fact that the most efficient part of the visible spectrum is not the 

 same for all heliotropic organisms. It is known through Blaauw's 

 experiments that the heliotropic curvatures of the seedling of 

 oats are produced most rapidly in the blue part of the carbon arc 

 spectrum. This should force Hess either to the conclusion that 

 the seedlings of oats do not suffer from total color blindness, 

 since the most efficient part of the spectrum for the totally color 

 blind is in the yellowish-green; or to the assumption that onh' 

 plants are heliotropic, but that animals which show the same 

 reactions to light are not heliotropic. Hess chooses the second 

 alternative by stating that plants are heliotropic, while animals 

 are 'lamprotropic' (Xa/xTrpos^- (bright), ^^ i.e., in plants the helio- 

 tropic curvature occurs purely automatically, while animals 

 bend or move to the source of light because it is 'bright.' It 



^ V. Frisch. Der Farbensinn und Fonnensinn der Biene, Zool. .Jahrb., 1914, 

 3.5, 1, Abt. f. allg. Zool. u. Physiol. 



* V. Frisch and Kupelwieser. Biol. Centralbl., 1913, 33, 517. 

 'Ewald. Ztschr. f. Psychol, u. Physiol, d. Sinnesorg., 1914, 48, Abt. 2, 285. 

 i» Hess, loc. cit., pp. 708 and 709. 



