MiNKlEWicz, Chroniotropism and Phototropism 9 1 



A. GENERAL BIOLOGY. 



1. One may find animals chromotropic with reference to the middle rays of 

 the spectrum, each ray having its own specific action. Indeed Daphnia, according 

 to Paul Bert and J. Lubbock, is xantho-chlorotropic, a fact which is absolutely 

 incompatible with the theory of Loeb ('90). 



2. Purpurotropism is not necessarily connected with positive phototropism 

 nor erythrotropism with negativ^e phototropism. One may find animals which 

 behave in the reverse manner. This is proved by the excellent experiments of 

 Engelmann upon unicellular organisms (1882 and 1883). According to him 

 Paramecium bursaria, which is positively phototropic, avoided the green and the 

 blue and directed itself toward the red. Likewise Navicula (a diatom) ceased 

 movement in darkness and in the green. 



3. Organisms should exist which, while being positively or negatively photo- 

 tropic are not at all chromotropic (total tropic blindness; that is achromotropy), 

 as Lineus is during the transitory stages of inversion. 



4. There are organisms like the plants studied by J. Wiesner ('79) which are 

 insensitive to certain rays of the spectrum (partial tropic blindness; that is, the 

 axanthotropy of Vicia sativa). 



5. It follows from the vertical tube experiments upon the zoea larvae that the 

 chromatic rays may have a certain influence upon the vertical distribution of aquatic 

 animals, granting the unequal absorption of the different rays of the spectrum, 

 the greatest for the red, the least for the blue (W. Spring, H. Fol, E. Sarasin, 

 Forel). 



B. psycho-physiology. 



The experiments which I described in my preceding note lead me to believe 

 that in studying the biology of the lower animals one should seek the indices which 

 may point the way to an explanation of the complex and difficult phenomena of 

 vision. 



1. Chromotropism being independent of phototropism, it seems to me that 

 the perception of white light may be a primitive phenomenon, much more simple 

 than it is generally believed to be and independent of chromatic perception (this 

 is corroborated by the well known experiments of A. Charpentier, and also by 

 the historic fact that in the best theory of vision, Hering was forced to admit the 

 existence of a special white-black substance). 



2. It seems superfluous and futile to seek for the solution of the problems of 

 chromatic vision in the hypothetical creation of different nerve fibers (Young- 

 Helmholtz), of various pigment granules (A. Pizon), or of different chemical sub- 

 stances (Hering), endowed with specific sensitiveness for different rays of the 

 spectrum. One should rather ask whether there are not different physiological 

 states in the same living substance which give rise to these complex phenomena of 

 chromatic vision, as in Lineus the different states artificially induced bring about 

 all the successive and transitory stages of chromotropism. [Experiments of Per- 

 gens and further of Lodato ('00) upon the chemical phenomena in the retina, 

 the intensity of which varies according to the action of different rays of the spec- 

 trum.] 



