INSTANCES AND CAUSES OF LUMINOSITY 383 



wide distribution of the germs 1 . The germs grow well in a decoction of fish to 

 which one or two per cent, of peptone, of sodium and magnesium chlorides, and if 

 necessary of glucose, have been added. By the addition of gelatine or agar solid 

 media may be produced. 



Meyen observed luminous masses containing numerous colourless Oscillaria 

 filaments in the Atlantic, and Ehrenberg states that the Diatoms Chaetoceras and 

 Discoplea are self-luminous 2 , but it is possible that the light was produced by 

 adherent Bacteria 3 . 



Fungi. Retzius and von Humboldt 4 showed that the long-known luminosity 

 of wood was due to parasitic Fungi. The sclerotium (Rhizomorphd) of Agaricus 

 melleus, and the finer mycelium of Xylaria hypoxylon are commonly responsible for the 

 peculiarity. It is usually sufficient to keep wood destroyed by Fungi, especially that 

 of the root, in a damp chamber for it to become luminous 5 . The mycelium of 

 Agaricus melleus when grown in a fluid nutrient medium gives out a considerable 

 amount of light 6 , and the mycelia and fruit bodies of both Ascomycetes and of 

 Hymenomycetes may become luminous when grown on artificial media. 



The gill lamellae of Agaricus olearius 7 which grow on old olives in S. Europe, 

 phosphoresce strongly, as does also the remainder of the sporophore, but less 

 strongly. In the tropics many forms seem to be strongly luminous, such as 

 Agaricus Gardneri* (Brazil), A. igneus* (Amboina), A. noctilucens (Manila). 



The older observations upon the production of flashes of light by leaves, flowers, 

 and so forth are probably the result of optical illusions 11 , but the St. Elmo's fire 

 produced by electrical radiation may occur on plants. According to Mornay and 

 Martius, certain Euphorbias have luminous latex, the latter possibly undergoing 

 oxidatory photo-chemical changes on exposure to air, or becoming impregnated with 



I Molisch, Bot. Ztg., 1903, p. 17, always found Micrococcus phosphoreus (Syn. == Bac t. phospho- 

 rescens Beyerinck). 



3 Meyen, Physiol., 1838, Bd. n, p. 202. Cf. Ludwig, Centralbl. f. Bact., 1887, Bd. n, p. 402 ; 

 Ehrenberg, Die das Funkeln u. Aufblitzen des Mittelmeeres bevvirkenden kleinen Lebensformen, 

 1874, p. 3 (reprint from Festschr. d. Ges. naturf. Freunde zu Berlin). 



3 Dubois (Le9ons de Physiologic, 1898, p. 451) has given up his earlier statement that the 

 phosphorescence of Pholas dactylus (the rock-boring mollusc) was due to a symbiotic Bacterium. 



4 See Agardh, Allgem. Biol. d. Pflanzen, 1832, p. 179; de Candolle, Pflanzenphysiologie, 1835, 

 Bd. II, p. 680, footnote; P. Heinrich, Phosphorescenz der Korper, 1811. 



5 For literature and facts see Ludwig, Ueber d. Phosphorescenz d. Pilze u. d. Holzes, 1874 J 

 Lehrbuch d. niederen Cryptogamen, 1892, p. 525. Hitherto no luminous bacteria have been found 

 to cause the luminosity of wood. 



6 Brefeld, Bot. Unters. ii. Schimmelpilze, 1877, Heft iii, p. 170. 



7 Fabre, Ann. sci. nat., 1855, 4 e ser., T. iv, p. 179 ; Tulasne, ibid., 1848, 3 se>., T. IX, p. 541. 

 Cf. also Ludwig, I.e., 1874, p. 9. The light is evolved before the development of the hymenium, 

 and it ceases before the collapse of the tissues. Cut surfaces may also be luminous. 



8 Gardner, quoted by Ludwig, 1. c., 1874, p. 9. 



9 Rumph, Herbarium amboinense, 1750, Bd. vi, p. 130. 

 10 Gaudichaud, quoted by Ludwig, I.e., 1874, P- 9- 



II For literature see Fries, Flora, 1859, P- J 7 8 5 Meyen, Pflanzenphysiologie, 1838, Bd. u, p. 200 ; 

 Ludwig, I.e., 1874, p. 5; Crie", Compt. rend., 1881, Bd. xcrii, p. 853; Ascherson, Naturwiss. 

 Wochenschrift, 1901, p. 106. Senebier (Physiol. vegetal., 1800, T. in, p. 315) states that the 

 spadix of Arum maciilatum phosphoresces when placed in oxygen. 



