3i 6 THE FOOD OF PLANTS 



to Schunk and Marchlewski (1. c.) definite products, chlorophyllan and alkali-chloro- 

 phyll respectively, may be obtained from chlorophyll by treatment with acids and 

 alkalies. The granular or acicular brown deposits of ' Hypochlorin ' observed by 

 Pringsheim were produced in green tissues when they were treated with hydrochloric 

 acid, and according to Meyer and Tschirch ' these deposits were composed mainly 

 of chlorophyllan. 



Marchlewski is convinced that the chlorophyll isolated from the most various 

 plants is in all cases identical, but nevertheless various compounds of chlorophyll may 

 exist in the living chloroplastid, while it is not even known whether chlorophyll exists 

 in the chloroplastid in dissolved form, and whether it is chemically or mechanically 

 united with the latter. The fact that the spectrum of a living chloroplastid agrees 

 with that of isolated chlorophyll, allowing for the disturbance caused by the solvent 

 medium, does not afford conclusive evidence one way or the other 2 . The trifling 

 spectroscopic differences which extracts from different plants may exhibit are not 

 necessarily due to the presence of specifically distinct forms of chlorophyll, but 

 may be due to impurities, to decomposition products, or to the influence of the 

 solvent medium. There is apparently a chemical relationship between chlorophyll 

 and haemoglobin, for both, according to Schunck and Marchlewski, are derivatives 

 of Pyrrol, and exhibit also certain spectroscopical similarities 3 . 



Yellow pigments. The yellowish-red pigments are by no means all identical 

 chemically or spectroscopically, but they all seem to belong to the group of carotins. 

 The typical carotin pigment appears to be present in all chloroplastids, whether 

 green or differently coloured, and many of the supposed varieties are probably 

 only impure extracts. It is impossible to say at present whether this is universally 

 the case, or whether etiolin, protochlorophyll, haemotochrome, &c., are special 

 forms of carotin or carotin compounds. It is still doubtful whether chlorophyll 

 is formed directly from one or other of these yellow pigments 4 . This would 

 only be possible by a profound chemical change, for carotin is a hydrocarbon 

 (Marchlewski, 1. c., p. 73), whereas chlorophyll is a differently constituted nitrogen- 

 containing body, so that if any one of the yellow pigments is converted into 

 chlorophyll simply by contact with air, it can hardly be a carotin compound. 

 The yellow pigments are usually obtained by agitating an alcoholic extract of leaves 

 with dilute potash, and according to Molisch yellow crystals may be obtained 

 from green tissues by similar treatment 5 . 



1 Cf. Hansen, 1. c., 1889, p. 38. 



- Marchlewski, 1895, I.e., p. 63. Monteverde (I.e., 1893, p. 176) and Etard (Compt. rend., 

 '895) T. cxx, p. 275) assume that many varieties of chlorophyll exist. G. Kraus, 1872, 1. c., p. 47 ; 

 Hansen, 1. c., 1879, P- 77> an d 1893, 1. c., p. 294; Reinke, Bot. Zeitung, 1886, p. 196; Monteverde, 

 I.e., 1893, p. 134. 



3 Schunck und Marchlewski, I.e., 1894, p. 288; Tschirch, I.e., 1896, p. 92 ; Nencki, Mem. d. 

 sci. biol. d. 1'Inst. Imp. d. M<fd. d. St.-Pe'tersbourg, 1897, T. v, p. 254. 



4 Hansen,!. c., 1889, p. 59; Monteverde, I.e., 1893, p. 186; Schrotter-Kristelli, Bot. Centralbl., 

 1894, Bd. LXI, p. 33; Marchlewski, 1895, I.e., p. 71 ; Molisch, Ber. d. Bot. Ges., 1896, p. 18 ; 

 Tschirch, ibid., 1896, p. 85 ; Zopf, Biol. Centralbl., 1895, Bd. xv, p. 418. Cf. \Viesner, Entstehung 

 d. Chlorophylls, 1877, p. 25. 



"' Molisch, Bcr. d. Bot. Ges., 1896, p. 18. 



