STRUCTURE AND PROPERTIES OF THE CHLOROPLAST1D 315 



Chromatophores are built up of a variety of substances, mainly proteid 

 in nature l , and in chloroplastids a little chlorophyll is always present, but 

 even when the colour is a deep green it does not exceed o-i per cent. 2 

 Yellow pigments from the carotin group seem never to be absent, even 

 from etiolated chloroplastids or from those of red and brown seaweeds 3 . 

 Many of these pigments are soluble in water, but chlorophyll and carotin 

 are exceptional in this respect, so that treatment with hot water suffices to 

 render the presence of chlorophyll immediately evident 4 . Except in 

 etiolated chloroplastids, chlorophyll is present in all cases where carbon 

 dioxide assimilation is possible. 



Although the conspicuous colour of chlorophyll naturally first attracted 

 attention to the chloroplastids, it is simply an accessory part of the latter, 

 and attains physiological importance only in connexion with the living 

 plastid (p. 304), for the chemical properties of the chlorophyll alone do 

 not suffice to explain the problem of carbon dioxide assimilation, although 

 they must have important bearings upon it. It is not, however, our 

 purpose to give a detailed account of the chemical and optical properties 

 of chlorophyll, and a reference to the literature of the subject must suffice 5 . 

 In Sect. 60 those optical properties which are of importance in connexion 

 with the assimilation of carbon dioxide will be mentioned. 



The isolated chlorophyll pigment 6 contains nitrogen but no iron 7 . According 



1 Cf. Sect. II ; also Zimmermann, Zelle, 1887, p. 60, and Beihefte z. Bot. Centralbl., 1894, p. 90, 

 where the work of Zacharias and Schwarz is also mentioned. Oil is apparently never absent, and in 

 certain cases is especially abundant. It may serve as a solvent for the chlorophyll. Zimmermann, 

 Zelle, p. 61 ; Schmitz, Chromatophoren d. Algen, 1882, p. 60 ; Engelmann, Bot. Zeitung, 1883, p. 21 ; 

 Schimper, Jahrb. f. wiss. Bot., 1885, Bd. XVI, p. 188; A. Meyer, Bot. Zeitung, 1885, p. 433. On 

 the presence of Cholesterin, see Reinke, Ber. d. Bot. Ges., 1885, p. Ivi ; Hansen, Farbstoffe d. Chloro- 

 phylls, 1889, p. 60. 



2 Tschirch, Pflanzenanat., I, 1889, p. 57. 



3 Found in Florideae by Rosanoff (Me 1 , d. 1'Acad. d. 1. Soc. Imp. d. Cherbourg, 1867, T. xm, 

 p. 302) ; in Fucaceae by Millardet (see G. Kraus, Zur Kenntniss d. Chlorophyllfarbstoffe, 1872, 

 p. 106). Cf. Hansen, Stoffbildung b. d. Meeresalgen, 1893, pp. 263, 292, &c. A similar red colour 

 is assumed by certain plants when observed through solutions of fuchsin or potassium permanganate 

 (Hansen, I.e., 1893, p. 299; Noll, Flora, 1893, p. 27). On the simultaneous presence of yellow 

 pigments, cf. Monteverde, Acta horti Petropolitani, 1893, Vol. xm, p. 176. On Neottia, cf. Lindt, 

 Bot. Zeitung, 1885, p. 825. 



* Cf. Reinke, Bot. Zeitung, 1886, p. 177. 



8 Literature : G. Kraus, Zur Kenntniss d. Chlorophyllfarbstoffe, 1872 ; A. Meyer, Das Chlo- 

 rophyllkorn, 1883; Tschirch, Unters. ii. das Chlorophyllkorn, 1884; Hansen, Farbstoffe des 

 Chlorophylls, 1889; Monteverde, Das Absorptionsspektrum des Chlorophylls, 1893 (Sep.-abdr. a. 

 Acta horti Petropolit., Vol. xm), and on Protochlorophyll, 1894 (ibid.) ; Schunck u. Marchlewsk, 

 Ann. d. Chemie, 1894, Bd. CCLXXVIII, p. 329, and Annals of Botany, 1889-90, Vol. Ill, p. 65; 

 Marchlewski, Die Chemie d. Chlorophylls, 1895 ; Tschirch, Ber. d. Bot. Ges., 1895, p. 76. 



6 [Nehemiah Grew (Anatomy of Plants, 1682, p. 273) extracted green and yellow pigments from 

 leaves by means of oil, and apparently also observed the fluorescence of chlorophyll.] 



7 Molisch, Die Pflanze in ihrer Beziehung zum Eisen, 1892, p. 85. On the necessity of iron for 

 the formation of chlorophyll, see Sect. 74. 



