326 LIGHT AND THE BEHAVIOR OF ORGANISMS 



3. Verworn's Experiments 



The experiments of Verworn (1889) yielded results 

 which led him to conclude that the diatom Navicula bre- 

 vis reacts only to the shorter waves, while Oscillaria reacts 

 to all the waves in the visible spectrum. " Als die allein 

 wirksamen Lichtstrahlen erwiesen sich auch bei den Dia- 

 tomeen die kurzwelligen " (p. 49); " Die Versuche, welche 

 sich auf die Ermittelung der wirksamen Strahlen bezogen, 

 hatten das ganz unvermuthete Ergebniss, dass Strahlen 

 von alien Wellenlangen ungefahr von der Linie a bis 

 iiber G hinaus die Bewegungen der Oscillarien beeinflussen. 

 . . . Die Ansammlungen der Oscillarien war nach Ein- 

 schaltung von Rubinglas oder Kalibichromatlosung, auch 

 im Halbdunkel, ebenso vollkommen, wie bei Anwendung 

 von griinem Glas, Kobaltglas, Kupferoxydammoniaklosung 

 oder reinem Sonnenlicht " (p. 51). In these experiments 

 Verworn mounted the organisms on a slide and studied the 

 movements under a microscope, surrounded by a tight case 

 which was black inside. The case contained an opening 

 15 X 20 mm. in one side to admit light. Colored glass 

 plates or flat flasks containing different solutions could be 

 so adjusted as to admit only light which passed through 

 them. The colored media used were thoroughly tested 

 spectroscopically (" genau spektroskopisch untersucht "). 

 Five different media were used. The red glass transmitted 

 red and orange (600-740"") ; the cobalt glass, blue and violet 

 (410-510"") and a little infra-red; the green glass, yellow 

 and green, and a little orange and blue (480-600^''') ; the 

 potassium bichromate solution, red, orange, yellow, and a 

 little green (550-740"") ; and the ammoniacal solution of 

 copper hydrate, blue and considerable green (430-520^0- 



The Oscillaria were positive; they collected at the side 

 nearest the light, even if it was of very low intensity 

 (" Halbdunkel "), no matter which one of the media was 

 in the opening. The diatoms, on the other hand, moved 

 toward the light only in the shorter waves; they did not 



