14 PHYSIOLOGY or NUTRITION 



serves attention: Timiriazeyi obtained this by the action of nascent hydrogen. 

 ' It is yellow or red in solution, according to the concentration. It is very easily 

 oxidized, going over into chlorophyll; for this reason it must be preserved .under 

 carbon dioxide or hydrogen in sealed tubes. It is stable in hydrogen, in light 

 as well as in darkness, but in carbon dioxide it is stable only in darkness; in 

 light, with carbon dioxide, it becomes green and is transformed into chlorophyll. 

 It must be supposed that carbon dioxide is decomposed in this case and that 

 oxygen is liberated, at the expense of which the transformation and greening of 

 the protophyllin occurs. Absorption bands in the orange and green regions of 

 the spectrum, corresponding to bands II and IV of chlorophyll, are character- 

 istic of protophyllin. 



It appears from many investigations that the formation of chlorophyll in 

 plants is a very complicated process. Until the publication of the work of 

 Liro^ most authors failed to distinguish between the beginning of chlorophyll 

 formation and the visible accumulation of this pigment in plants as they become 

 green. This distinction is quite necessary. 



We shall first turn our attention to the conditions requisite for the formation 

 of chlorophyll. Light may be mentioned as the first of these. Leaves of angio- 

 sperms grown in darkness are always yellow, but such etiolated plants soon turn 

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

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

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

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

 light of medium intensity is most favorable. Famintsyn^ 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 difiuse light. 



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

 chlorophyll, a matter which was carefully investigated by Wiesner.* He em- 



1 Timiriazeff, C, La chlorophylle et la reduction de I'acide carbonique par les v6g6taux. Compt. 

 rend. Paris J02: 686-689. 1886. Idem, La protophylline dans les plantes etiol«es. Ihtd. 109: 414-416. 

 1889. Idem, La protophylline naturelle et la protophylline artificielle. /ifd. 120: 467-470. 189s. 



2 Lire, J. Ivar, Ueber die photochemische Chlorophyllhildung bei den Phanerogamen. Ann. Acad. 

 Sci. FennicBe (Helsinki) Ai : 1-147. 1909. 



» Lubimenko, W., Influence de la lumiSre sur le d«veloppement des fruits et des graines chez les vfgMaux 

 superieurs. Rev. g^n. bot. 22: 145-175. 1910. 



« Artari, A., Ueber die Entw.icklung der grflnen Algen unter Ausschluss der Bedingungen der Kohlen- 

 saure-AssJmilation. Bull. Soc. Imp. Nat. Moscou 13 : 39-47. 1900. Idem, Zur Em&hrungs-physiologie 

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



'Famintzin, A., Die Wirkung des Lichts auf das Ergunen der Pflanzen ("aus dem Bulletin :io 548- 

 552.")- Melanges biol. Acad. Imp. Sci. St.-P6tersbourg 6 : 94-100. 1866. 



• Wiesner, Julius, Untersuchungen aber die Beziehungen des Liohtes zum Chlorophyll. Sitzungsber. 

 (math..naturw Kl.) K. Akad. Wiss. Wien 69^: 327-385. 1874. Idem, Die Entstehung des Chloro- 

 phylls m der Pflanze. Wien, 1877. 



