ASSIMILATION OF CARBON 



15 



green when exposed to light. Seedlings of some conifers, 1 young fern fronds and 

 some one-celled algae 2 are exceptions, for they become green in darkness; still, 

 according to Liubimenko, conifer seedlings form much less chlorophyll in dark- 

 ness than in light. Very weak light is sufficient for chlorophyll formation, and 

 light of medium intensity is most favorable. Famintsyn 3 exposed a part of an 

 etiolated plant to direct sunlight, while the intensity of the light falling upon the 

 remaining portion was reduced by interposing sheets of paper; greening always 

 occurred first in the reduced light. According to Wiesner this phenomenon is 

 to be explained by supposing that decomposition and formation of chlorophyll 

 occur simultaneously. In light of low or medium intensity the decomposition 

 process is nearly absent, while in strong light active formation is, accom- 

 panied by rapid breaking down of chlorophyll, which results in less pronounced 

 greening than occurs in diffuse light. 



Various parts of the spectrum have different effects upon the formation of 

 chlorophyll, a matter which was carefully investigated by Wiesner. 4 He 

 employed double-walled bell-jars with colored liquids, as light screens for isolat- 

 ing certain regions of the spectrum (Fig. 8). Solutions of 

 potassium dichromate and of ammoniacal copper oxide 

 [copper sulphate solution to which an excess of ammonia 

 water is added] were most frequently used; the first, in 

 medium concentration, permits the passage of the rays of 

 the less refrangible half of the spectrum (red, orange, 

 yellow and a part of the green), while the second trans- 

 mits the remainder of the visible rays (the rest of the green 

 and all of the blue and violet). Thus, by the use of these 

 liquids, the spectrum is separated into two parts. [Of 

 course the intensity of the light transmitted is consider- 

 ably decreased.] 



In weak light plants become green sooner under the 

 yellow solution, but in strong light more quickly under the 

 blue. This may be explained by supposing that in weak 

 light the formation of chlorophyll occurs almost exclusively, 

 under the influence of the less refrangible rays, which are most favorable, while 

 in strong light, besides chlorophyll formation, an active decomposition also takes 

 place. Experiments upon the decomposition of alcoholic solutions of chlorophyll 

 under colored bell- jars have shown that this process is especially pronounced in 

 the less refrangible half of the spectrum; greening in plants is thus seen to be 

 weaker in strong yellow-red light because a very rapid destruction here accompa- 



1 Lubimeako, W., Influence de la lumiere sur le developpement des fruits et des graines chez les vegetaux 

 superieurs. Rev. gen. bot. 22 : 145-175. 1910. 



Artari, A., Ueber die Entwicklung der griinen Algen unter Ausschluss der Bedingungen der Kohlen- 

 saure-Assimilation. Bull. Soc. Imp. Nat. Moscou 13 : 39-47. 1900. Idem, Zur Ernahrungs-physiologie 

 der griinen Algen. Ber. Deutsch. Bot. Ges. 19: 7-9. 1901. 



3 Famintzin, A., Die Wirkung des Lichts auf das Ergriinen der Pflazen (" aus dem Bulletin 10: 548- 

 552.") Melanges biol. Acad. Imp. Sci. St.-Petersbourg 6: 94-100. 1866. 



1 Wiesner, Julius, Untersuchungen iiber die Beziehungen des Lichtes zum Chlorophyll. Sitzungsber. 

 (math.-naturw. Kl.). K. Akad. Wiss. Wien 691: 327-385. 1874. Idem, Die Entstehung des Chloro- 

 phylls in der Pflanze. Wien, 1877. 



)M. 



M_^ 



Fig. 8. — Double- 

 walled bell-jar with 

 colored solution filling 

 the space between 

 the walls. 



