10 CARL VON HESS 



If the tropisms were identical, the plants placed between the 

 colored papers should behave in relation to these in exactly the 

 same manner as animals under like conditions. If, however, the 

 heliotropism of plants differs from that of animals as much as 

 the curves indicate, then, if we carefully choose a green surface 

 and a blue, place animals and plants between the two, the 

 former will go to the green side and the plants will bend toward 

 the blue in exactly opposite directions. This behavior is indeed 

 quite marked as you see by the samples set before you. The 

 plants bend over to the blue often in one to two hours after 

 being placed in position. 



I have taken the liberty of briefly introducing to you two new 

 methods for the investigation of the heliotropism of plants, 

 because I believe they may do good service in botanical experi- 

 ments and elsewhere, especially in quantitative experiments, and 

 because particularly the second method may easily be handled 

 by amateurs, and gives marked results, besides being well suited 

 to use in the lecture room. As to the pertinent scientific ques- 

 tions, these I have touched upon today only in so far as the 

 often repeated assertions of Loeb, that animal and plant helio- 

 tropism is identical, required a final refutation. 



V 



In conclusion, let me add a word on my discoveries about the 

 sight qualities of fish and invertebrates. Zoologists and botan- 

 ists have again and again declared they cannot acknowledge 

 my ' theories ' (as they call them) because they stand in too 

 harsh contradiction to the prevailing doctrines. The truth of 

 the matter is, that I have never set up any theory whatever, 

 but have made known only facts which every conscientious 

 observer may easily verify for himself. What Sprengel pro- 

 mulgated in 1793, and has been taught ever since about the 

 connection between the coloring of flowers and the visits of 

 insects, was a theory. This theory is now finally done away 

 with, for it is built upon demonstrably wrong surmises as to 

 the sight qualities of bees. Plant biology, for a hundred years 

 and more under the ban of this doctrine, which even Darwin 

 believed to be true, will now needs turn to the task of ascer- 

 taining the real meaning of the splendor of color in blossoms. 



