384 THE PRODUCTION OF HEAT, ALIGHT, AND ELECTRICITY 



luminous Bacteria 1 . There is also always a possibility that the phenomenon is one 

 of fluorescence, light rays absorbed during the daytime being emitted at night. The 

 glimmering of the protonema of Sckizostega, on the other hand, is simply due to the 

 collection of the feeble rays of light by the lens-shaped cells of the protonema 2 . 



Uses. Although it is possible that the luminous sporophore of a Fungus may 

 attract night-flying insects, and so aid in the dissemination of the spores, it is not 

 easy to see what use the luminosity of Bacteria or of a mycelium in wood could have. 

 The presence of luminous Bacteria on a dead fish may attract fishes which swallow 

 the Copepoda and other forms which devour the Bacteria, and in the dark depths of 

 the ocean the luminous properties of an organism acquire greater importance. 



The production of light is a physiological process dependent upon 

 respiration, and, like the latter, it continues in darkness 3 . We are dealing, 

 therefore, with a chemical production of light 4 , and not with a fluorescent 

 emission of light rays previously absorbed. The production of light usually 

 begins in Fungi at a certain stage of development and then spreads to all 

 parts. Similarly, McKenney states that Bacteria become luminous only 

 at the end of the period of active locomotion. Under unfavourable conditions 

 the luminosity vanishes and it attains an optimum under definite conditions 

 as regards temperature, concentration, and food-supply. Luminosity, like 

 growth, decreases above the optimum temperature, and does not like re- 

 spiration and the production of heat increase up to the maximum 

 temperature. 



Luminosity, like locomotion and the production of pigments or 

 poisons, may be suppressed without fatal injury to the organism. Many 

 luminous forms have been grown at temperatures at which they produce 

 no light, and Beyerinck 5 has in fact found that certain forms appear to 

 become temporarily luminous under special conditions. 



When the conditions are favourable the light is emitted continuously, 



1 For literature see Meyen, 1. c., p. 203. 



2 Unger, Flora, 1834, p. 33; Noll, Arbeit, d. bot. Inst. in Wiirzburg, 1888, Bd. Ill, p. 477. 

 Ingenhousz (Versuche mit Pflanzen, German ed. by Scherer, 1786, Bd. I, p. 191) observed that the 

 vapours of ethereal oil excreted by the inflorescence of Dictamnns albus burst into flame when 

 a lighted match was brought near. 



3 Moderate light appears to exercise no effect upon the luminosity of Rhizomorpha. Cf. 

 Ltidwig, I.e., 1874, p. 26. Pfliiger and also McKenney (I.e., p. 222) obtained similar results with 

 Bacteria, but strong light, owing to its germicidal action, retards or inhibits the appearance of 

 luminosity. Cf. Tarchanoff, Compt. rend., 1900, T. cxxxi, p. 247; Suchsland, Centralbl. f. Bact., 

 2. Abth., 1898, Bd. iv, p. 714. 



4 Wiedemann, Ann. d. Physik u. Chem., 1889, N. F., Bd. xxxvn, p. 180; 1889, N. F., 

 Bd. xxxvin, p. 485 ; Wiedemann und Schmidt, Zeitschr. f. physik. Chemie, 1895, Bd. XVIII, p. 528 ; 

 Roloff, ibid., 1898, Bd. xxvi, p. 354; Winkelmann, Handbuch d. Physik, 1894, Bd. II, Abth. i, 

 p. 486. [Sudden crystallization may cause a liquid to glow with light, as, for instance, when salt is 

 precipitated in darkness by adding alcohol or concentrated hydrochloric acid to strong brine. This 

 is, however, hardly likely to be responsible for any appreciable production of light in the living 

 plant.] 



5 Beyerinck, Koninklijke Akad. v. Wetenschappen te Amsterdam, Oct. 1900, p. 359. 



