574 RADIATION BIOLOGY 



tant physiological processes in plants under natural conditions. An 

 example of such processes has been reported by Heimann (1950), who 

 stated that the guttation of Kalanchoe blossfeldiana changed in the same 

 rhythm as natural daylight and that it adapted itself if the intervals 

 between light and darkness were altered. He assumed that the primary 

 cause was to be found in the action of light on the permeability of the 

 protoplasm. 



INFLUENCE OF VISIBLE LIGHT ON PROTOPLASMIC STREAMING 



Pringsheim (1882) studied the protoplasmic streaming of Nitella, 

 Trade scantia, and Spirogyra and found that the streaming could be 

 started by light. Moore (1888), who used Vallisneria spiralis as the 

 test object, and Schroter (1905) and Andrews (1912), who used species 

 of Mucor, came to the same conclusion. Nothmann-Zuckerkandl (1915) 

 subsequently made a more detailed analysis of the question. His tests 

 were made on leaves of Elodea and Vallisneria, the stamen hairs of 

 Tradescantia, and the root hairs of Hydrocharis. Gaslight or an arc lamp 

 was used as the source of light, the heat rays being removed with various 

 forms of filters. His experiments showed the existence of certain quanti- 

 tative associations between the reaction and the strength or quantity of 

 light. The stronger the light, the more rapidly did the protoplasmic 

 streaming start, and the longer were the aftereffects of illumination. 

 Illumination with an arc lamp for 2-5 min started a streaming that con- 

 tinued for 6-24 hr. The accuracy of these conclusions was later eon- 

 firmed by Fitting (1925). The reaction was also found to be dependent 

 on the wave length of the light. Nothmann-Zuckerkandl compared dif- 

 ferent wave-length ranges after the light had been screened off to the 

 same strength (measured with a thermoelement). He found that red 

 and infrared hght had the greatest effect, that the other kinds of rays 

 were less active, and that their effect diminished with the wave length. 



Beikirch (1925) and vSchweickerdt (1928) also studied the influence 

 of various kinds of light. They were, however, only able to confirm 

 Nothmann-Zuckerkandl's results with regard to red light, which they 

 also found to be most active. On the other hand, they found infrared 

 light to be inactive, and Schweickerdt's experiments with V. spiralis 

 revealed no parallelism between the influence of the kind of light and 

 the wave length. It was found that blue light and then green had, after 

 red light, the strongest effect. 



Protoplasmic streaming ceases in the dark and starts again on illumi- 

 nation (Schroter, 1905; Nothmann-Zuckerkandl, 1915). Schweickerdt 

 (1928) showed that the streaming also ceases in red and in green light 

 when illumination has continued for some time and that its rate decreases 

 with continuous weak illumination with white and blue light. The 



