330 



SCIENCE 



[N. S. Vol. XLI. No. 1052 



of sensitiveness in the blue (in the neighbor- 

 hood of A, =• 4:71 [jLfj.), the other in the yellowish- 

 green (in the region of A = 534/t;a). The 

 latter type is found in Chlamydomonas, 

 Daphnia, the larvae of barnacles and other 

 organisms; the former type exists in Euglena, 

 Eudendrium, the seedlings of oats and others. 



It seems of interest to call attention to the 

 fact that according to the measurements of 

 Trendelenburg the visual purple in the eye of 

 the rabbit is bleached most rapidly by light 

 of the wave-length A==536/i/i. As Kuehne 

 had already shown, visual purple is not affected 

 by red light, and only feebly by yellow light. 

 The relative efficiency of different parts of the 

 spectrum for the heliotropic reactions of 

 Chlamydomonas coincides, therefore, approxi- 

 mately with the relative bleaching power of 

 rays of different wave-lengths for visual purple. 

 This makes it almost appear as if in the one 

 group of organisms, namely, those which be- 

 have like Daphnia or Chlamydomonas, the 

 heliotropic reactions were determined by a sub- 

 stance or by substances which behave in regard 

 to photosensitiveness like visual purple; and 

 which may possibly be identical with visual 

 purple. 



This assumption allows us to explain the 

 heliotropic reactions of lower organisms with- 

 out arbitrarily ascribing to them sensations 

 of brightness the existence of which can in 

 their case not be proved. And, furthermore, 

 when the heliotropic effect of rays of different 

 wave-lengths upon lower organisms is found 

 to run parallel to their effect upon the bleach- 

 ing of visual purple (as it does in Daphnia 

 and Chlamydom,onas) it seems more rational 

 and promising to conclude that the heliotrop- 

 ism in these eases is caused by a substance or 

 substances which behave photochemically like 

 visual purple than that these lower organisms 

 suffer from total color-blindness. We have 

 already shown in our first note that the theory 

 of heliotropic orientation is independent of 

 the relative efficiency of different wave-lengths. 



We may summarize the results of our experi- 

 ments in the following way : 



1. The validity of the Bunsen-Eoscoe law 

 for the heliotropic reactions of certain (and 

 possibly all) plants and animals suggests that 



these reactions are due to a chemical action, 

 of the light. 



2. There seem to exist two types of helio- 

 tropic substances, one with a maximum of 

 sensitiveness (or absorption) in the yellowish- 

 green (near X = 534 fifi) , and the second with 

 a maximum of sensitiveness in the blue (near 

 A = 47Y/Aju). Visual purple is a representa- 

 tive of the former type. 



3. The photosensitive substance of the visual 

 purple type occurs in the protozoan Chlamy- 

 domonaSj which is usually stated to be a plant, 

 in Daphnia and many other organisms. The 

 photosensitive substance with the maximal 

 sensitiveness in the blue is found in Euglena, 

 in many plants and in certain animals, e. g., 

 Eudendrium. and probably others.^ 



4. It would, therefore, be wrong to state that 

 the one type of photosensitive substances is 

 found exclusively in plants and the other ex- 

 clusively in animals. As a matter of fact they 

 are distributed independently of the syste- 

 matic boundaries between the two groups of 

 organisms. 



5. It is immaterial for the theory of helio- 

 tropism to which of the two types the photo- 

 sensitive substance in any given heliotropic 

 organism belongs. Jacques Loeb, 



Haedolph Wastenets 

 The Eockefellee Institute 

 POK Medical Ee search, 

 New York 



AMEBIC AN ASSOCIATION FOB THE AD- 

 VANCEMENT OF SCIENCE 



SECTION M, AGRICULTURE 



The first meeting of Section M, Agriculture, of 

 the American Association for the Advancement of 

 Science, was held in the Engineering Building of 

 the University of Pennsylvania, Philadelphia, De- 

 cember 30, 1914. 



The inauguration of the new section was par- 

 ticularly auspicious, and the large attendance was 

 encouraging as indicating wide interest. Dr. 

 Charles W. Eliot, president of the Association, 

 presided at the opening of the meeting, and in a 

 brief address called attention to the great impor- 

 tance of the agricultural industry, and expressed 



5 This seems to be indicated by the work of 

 Parker and his pupils. 



