PIGMENTS 497 



organs of Prunella grandiflora are abnormally shaped and imperfectly coloured when 

 grown in darkness '. Red pigment is formed in the roots of Sah'jc, in many 

 rhizomes, hypocotyls, in the tentacles of Drosera, &c. 2 , only when they are exposed 

 to light, and in some cases only when the light is of considerable intensity, as in 

 Azolla, apples, and pears, for only the surfaces exposed to sunlight become red 3 . 

 Similarly, the autumnal colouration of leaves seems to be produced by the action of 

 light as soon as the vitality of the leaf-cells sink below a certain ebb, and the 

 change is hence frequently aided by a low temperature 4 , as is especially the case 

 with regard to the brown winter colouration of Conifers. The latter is characterized 

 by a partial or complete decomposition of the chlorophyll, and by a simultaneous 

 appearance of a brown or red pigment (Sect. 58) 5 . 



In a few non-chlorophyllous organisms, such as Micrococcus ochroleucus*", the 

 pigment is formed only in the light, while in Micrococcus prodigiosus and many 

 other bacteria its formation may be inhibited by conditions which still permit 

 of growth, such as strong illumination, sub-maximal temperatures, a deficiency of 

 oxygen, or the presence of poisonous substances. Spirillum rubrum, however, 

 forms coloured growths only when the oxygen supply is deficient, whereas when 

 leuco-products or chromogens are formed under such conditions, they rapidly 

 become coloured when oxygen is admitted 7 . The formation of pigment substances 

 may be suppressed most readily in bacteria, but in Phanerogams also the pigments 

 are secretory products, and hence the amount produced may alter or become a 

 vanishing quantity under special external conditions, which have, however, not as 

 yet been determined with certainty 8 . 



Schottelius, by exposing cultures to 41 C., obtained colourless races of Micro- 

 coccus prodigiosus which had at the same time lost the power of forming tri- 

 methylamine, and a similar result as regards the non-formation of pigment was 

 obtained by Phisalix with Bacillus pyocyanus, and by Laurent with the red Kiel 



1 Sachs, Bot. Zeitung, Beilage, 1863 and 1865, p. 117; Askenasy, Bot. Zeitung, 1876, p. i ; 

 Vochting, Jahrb. f. wiss. Bot., 1893, Bd. XXV, p. 177. Grapes: Laurent, Bull. d. 1. Soc. Bot. d. 

 Belgique, 1890, T. xxix, p. 71. 



2 Mohl, Vermischte Schriften, 1845, p. 390; Schell, Bot. Jahresb., 1876, p. 717; Pick, Bot. 

 Centralbl., 1883, Bd. xvi, p. 315 (seedlings) ; de Vries, Bot. Zeitung, 1886, p. 4 (Drosera) ; Kerner, 

 Nat. Hist, of Plants, 1894, Vol. I, p. 484 (Rhizomes). On algae, cf. Oltmann's Jahrb. f. wiss. Bot., 

 1892, Bd. xxin, p. 432. 



3 Senebier, Physik.-chem. Abh., 1785, iii. Th., p. 71 ; Askenasy, Bot. Zeitung, 1875, p. 498. 

 [In such cases as these, it is obvious that the red pigment has a protective function, and it can 

 hardly induce either transpiration or a rise of temperature above that of the surrounding medium in 

 roots of Salix, which turn red when exposed to light even though submerged in water.] 



4 Mohl, 1. c. ; Schiibler, Bot. Centralbl., 1886, Bd. xxvill, p. 205. 



5 [Schimper, 'Unters. liber die Chlorophyllkorper,' Jahrb. f. wiss. Bot., Bd. xvn, 885.] 



6 Prove, Cohn's Beitrage z. Biol., 1887, Bd. iv, p. 439. 



7 See Fliigge, I.e.; Lafar, I.e.; Dieudonne, Biol. Centralbl., 1895, Bd. XV, p. 108 ; Thuman, 

 Arb. d. Bact. Inst. in Karlsruhe, 1895, Bd. I, p. 291 ; Nicolle et Bey, Ann. d. 1'Inst. Pasteur, 

 1896, T. x, p. 669. For details on fungi: Elfving, Einwirkung d. Lichtes auf Pilze, 1890, p. 6; 

 Duclaux, Ann. d. 1'Inst. Pasteur, 1889, T. II, p. m. In lichens, pigments may be formed by the 

 co-operation of the symbionts. 



8 Nageli, Sitzungsb. d. Bair. Akad., 1879, p. 301; Hoffmann, Bot. Zeitung, 1881, p. 379; 

 Molisch, ibid., 1879, P- 49- 



PFFFFER K K 



