ASSIMILATION OF CARBON 1 9 



A rapid transformation of chlorophyllogen into chlorophyll occurs in living 

 plant cells under the influence of light. This process can also be observed in 

 plants that have been killed. According to Liro, if etiolated leaves are care- 

 fully killed so that at least some of the chlorophyllogen remains, and if they are 

 then exposed to light, some formation of chlorophyll can still be observed. For 

 the transformation of chlorophyllogen into chlorophyll, Liro and Isachenko 1 

 have shown that neither oxygen, favorable temperature conditions, nor even 

 the presence of carbohydrates are necessary, but since greening is possible only 

 with these conditions they are evidently necessary for the formation of chloro- 

 phyllogen, or of the chromogen that gives rise to it. Chlorophyll may be formed 

 from chlorophyllogen in the absence of light, as is exemplified by plants that 

 turn green in darkness; in such cases the influence of chemical agents must 

 replace the action of light. 2 



Such are the chief results of the researches thus far carried out upon chloro- 

 phyll and its formation. As to the role it plays in the chemical decomposition 

 of carbonic acid and the formation of the first products of photosynthesis 

 almost nothing is known. Schryver 3 suggests that the formaldehyde arising 

 in the decomposition of carbon dioxide and water enters into combination with 

 the chlorophyll.- 



As to the physics of the action of chlorophyll, it behaves as a sensitizer 4 and 

 renders the energy of the absorbed light effective in the decomposition of car- 

 bon dioxide. In an analogous manner the red light rays between lines B and C 

 of the spectrum rapidly decompose silver salts in the presence of chlorophyll, 

 although these salts are otherwise decomposed only by blue and violet rays. 



§4. Pigments Accompanying Chlorophyll. — Among the other pigments 

 accompanying chlorophyll, special attention should be given to carotin. 5 Boro- 

 din 6 was able to show that carotin (called erythrophyll by him) regularly ap- 

 peared in alcoholic leaf extract when he allowed this to form crystals under the 

 microscope. 



The chemical nature of carotin, and also some of the conditions of its forma- 

 tion in leaves, were first made clear by the investigations of Arnaud 7 and of 



1 Issatchenko, B., Sur les conditions de la formation de la chlorophylle. [Title and abstract in French, 

 article in Russian.] Bull. Jard. Imp. Bot. St.-Petersbourg 6: 20-28 [Abstract, p. 27-28]. 1906. Idem, 

 same title. Ibid. 7: 59-64 [Abstract, p. 64]. 1907. Idem, same title. Ibid. 9: 106-120 [Abstract, p. 

 119-120]. 1909. 



2 Monteverde and Liubimenko, 191 1. [See note 3, p. 18.] 



3 Schryver, S. B., Photochemical formation of formaldehyde in green plants. Chem. news 101 : 64. 

 1910. 



4 Tappeiner, H. von, Die photodynamische Erscheinung (Sensibilisierung durch fluoreszierende Stoffe). 

 Ergeb. Physiol. 8: 698-741. 1909. 



5 Escher, Heinr. F., Zur Kenntnis des Carotins und des Lycopins. Zurich, 1909. 104 p. (Zurich Poly- 

 techn. Dissert. 1909-10.) [For a general discussion of the yellow pigments, see Haas and Hill, 192 1. (See 

 note 3, p. 6.)] 



6 Borodin, J., Ueber krystallinische Nebenpigmente des Chlorophylls. Bull. Acad. Imp. Sci. St.- 

 Petersbourg 28: 328-350. 1883. 



7 Arnaud, A., Recherches sur les matieres, colorantes des feuilles; identite de la matiere rouge orange 

 avec la carotine, C18H24O. Compt. rend. Paris 100: 751-753- 1885. Idem, Recherches sur la composi- 

 tion de la carotine, sa fonction chimique et sa formule. Ibid. 102: 1119-1122. 1886. Idem, Sur la pres- 

 ence de la cholesterine dans la carotte; recherches sur ce principe immediat. Ibid. 102: 1319-1322. 1886. 

 Idem, Recherches sur la carotine; son role physiologique probable dans la feuille. Ibid. 109:911-914. 

 1889. 



