CH. vni] THE SIGNIFICANCE OF ANTHOCYANINS 127 



general metabolism, including translocation and fertilisation, to be 

 furthered by the warming effect of the pigment. 



The 'light-screen' hypothesis had no doubt a basis in the work of 

 Pringsheim. About 1880 Pringsheim 1 published the results of various 

 experiments on carbon assimilation, and among these, the effect of 

 light of different colours and intensities on chlorophyll. He found that 

 white light of a high intensity decolorised chlorophyll, but in red light 

 the effect was suppressed. In yellow, green, or blue light, on the 

 other hand, it is easy to decolorise and kill the cells of many Algae, 

 Characeae, Musci, Filices and Phanerogams. Thus in white light, 

 the result was attained in two or three minutes, in green and blue in 

 five minutes, whereas in red light of the same intensity and after twice 

 or four times as long exposure, no changes took place. Hence he sup- 

 poses the red rays to be photochemically inactive, or only very slightly 

 active, on plant cells. That the injurious effects were not due to heat 

 is shown by the fact that in green light the temperature did not rise 

 sufficiently to be harmful to plant cells. For instance even in red light, 

 the temperature of the water drop in which the tissue was placed, 

 was raised to over 45 C. within five minutes, and yet after 15-20 

 minutes' exposure, there was neither decolorisation nor death of the 

 cell. On the other hand, in green and blue light, cells were decolorised 

 and killed in five minutes, although after 15-20 minutes' exposure, 

 the water scarcely reached 35-36, a temperature quite harmless to the 

 cells. The solutions used were for red light, iodine in carbon bisulphide, 

 for yellow, potassium bichromate, for green, copper chloride, and for 

 blue, ammoniacal copper sulphate. 



It would seem, however, that Pringsheim may have overrated the 

 destroying effect of sunlight on chlorophyll, for Reinke 2 , in a paper 

 published in 1883, mentions some results he obtained by exposing both 

 the green and red (anthocyanin) parts of plants to light intensified by 

 a lens, the heat rays being cut off by a screen of alum solution. He 

 found that the chlorophyll in leaves of Elodea and Impatiens and the 

 red pigment in the petals of Papaver and Rosa were not decolorised 

 unless the light intensity became 800-1000 times greater than normal 



1 Pringsheim, N., 'Ueber Lichtwirkung und Chlorophyll! unction in der Pflanze,' 

 Jahrb. wiss. Bot., Leipzig, 1879-1881, xn; 1882, xm. Also ' Pringsheim's Researches 

 on Chlorophyll,' translated and condensed by Bayley Balfour, Q. /. Hicrosc. Sci., London, 

 1882, xxn, pp. 76-112, 113-135. 



2 Reinke, J., ' Untersuchungen iiber die Einwirkung des Lichtes auf die Sauerstoff- 

 ausscheidung der Pflanzen,' Bot. Ztg., Leipzig, 1883, XLI, pp. 697-707, 713-723, 732-738. 



