■~ MICHIGAN ACADEMY OF SCIENCE. 45 



by Sachs, and makes more general statements concerning the function. 

 There is no doubt, as Pfeffer states, that the rehitive activity has not 

 been precisely determined. It is not difificult to believe this, when one 

 considers the character of the apparatus used by Sachs, Pfetfer and 

 others to investigate the problem. 



For the following investigations to determine the effects of the differ- 

 ent portions of the solar spectrum, colored glass plates were secured: 

 red, yellow, green, blue, violet. These plates of glass were approxi- 

 mations towards a pure color. The plotted curve indicating the rela- 

 tive purity of these colors, is given in Science, Nov. G, 1903, p. 605. 

 Although they are not strictly speaking pure colors, yet they are, so 

 far as they go. definite, because the relative amount of other parts of the 

 spectrum, which passes through, are given, making it possible to decide 

 fairly in regard to the separate color-stimulus. The results obtained 

 from these particular glass plates, are, therefore, definite, and, for the 

 color combination, as indicated in the plotted curve, reliable, for the 

 functions mentioned. 



In giving the results of these investigations, the colors are arranged 

 in order, commencing with that producing greatest effect, and ending 

 with that producing least. The results for Phototropism and for de- 

 coloring of alcoholic solutions of chlorophyll, have already been pub- 

 lished (Sci., Xov. 0, 1903, p. GOl) but, for convenience, they are here 

 given. 



The results in regard to production of chlorophyll are taken from 

 Belzung, p. 77 ; and for assimilation of carbon dioxide, from Pfeffer, 

 p. 101, and Sachs, p. 176. The colors used by Belzung and Pfeffer may 

 not be exactly those here given. It is difficult to tell just the exact color 

 they used, because little or no description is given beyond that con- 

 tained in the mere term, — red, blue, etc. Therefore, a correlation of 

 results is not always possible. The double bell-jar method is a rather 

 crude one for several reasons, but particularly because it is impossible 

 to control the temperature and the ventilation. The colors here used 

 are, of course, not the only ones in the spectrum, but they are chosen as 

 being sufficiently distinct and well-known to convey a clear idea as 

 to what is meant. 



PHOTOTROPISM: 



Blue, white, violet, green, vellow, red, opaque. 

 DECOLORIXG OF CHLOROPHYLL, (alcholic solution): 



White, vellow, blue, red, violet, green, opaque. 

 PRODUCTION OF OXYGEN: 



White, vellow, green, red, violet, blue, opaque. 

 GROWTH: 



Opaque, red vellow, green, violet, white, blue. 

 PRODUCTION OF GREEN COLORING MATTER: 



White, vellow, green, blue, red, violet, opaque. (Gelzung) 

 ASSIMILATION OF CO,: 



* White, yellow, green, red, blue, violet, opaque. 

 *White, vellow, red-orange, green, blue, violet, opaque. 

 PHOTOTONIC AND FORMATIVE: 



White (?), violet, blue, green, yellow, red. (Pfeffer) 

 PHOTOT ACTIO: STEAMING OF PROTOPLASM: MOVEMENT OF -CHLORO- 

 PLASTS: 



Same as heliotropic, according to Pfeffer. 



These are: Violet, blue, red; none others ha\-ing effect. 



The results given above under phofotrojnsm show that Pfeffer's results are erroneous. 



*Both of these are given because thej' arise from different experiments, (Pfeffer.) 



