222 JACQUES LOEB AND HARDOLPH WASTENEYS 



would be difficult to invent a nicer example of reasoning in a 

 circle; since Hess's assumption that animals have the sensation 

 of brightness is based upon the fact that they move to the light . 



Yet we will try to follow Hess even into this circle and select 

 a case already mentioned in a previous note'^ and to which we 

 shall return in this paper, namely the case of two green flagel- 

 lates, Euglena viridis and Chlamydomonas pisiformis, which are 

 strongly heliotropic, but, being unicellular organisms, of course 

 have no eyes. For Chlamydomonas the place of greatest 

 efficiency in the spectrum is in the region of yellowish-green, 

 for Euglena it is in the blue. If we follow Hess we must logically 

 conclude from this that Chlamydomonas suffers from total color 

 blindness (although it has no eyes), that it is not heliotropic but 

 'lamprotropic,' and that it is an animal; while its cousin Euglena 

 has either a highly developed color sense or is heliotropic and is a 

 plant. 



Hess^^ thinks it is inconsistent for Loeb to deny the justifica- 

 tion of the assumption that all heliotropic animals are totally 

 color blind and at the same time to state that phenomena of 

 heliotropism are identical in animals and plants. Hess over- 

 looks the fact that the two statements rest on an entirely different 

 basis. The statement that positively heliotropic animals go to 

 the light because they are totally color blind is as we have seen 

 not a fact but an unnecessary and arbitrary assumption which 

 is in conflict with the facts and not even justifiable on the basis 

 of mere analogy, since totally color blind humans are not posi- 

 tively heliotropic. The fact that the region which is brightest to 

 the totally color blind human is at the same time most efficient 

 in certain heliotropic animals admits or demands, as we shall see, 

 an entirely different interpretation. 



On the other hand, the statement that heliotropic reactions in 

 animals and plants are identical is merely the expression of the 

 actual observations. Thus Loeb has been able to show that 

 sessile heliotropic animals react to one-sided illumination just 

 like sessile plants, namely by bending towards the source of 



" Scionec. 1015, 41, 328. 

 I- Lof fit., p. 700. 



