85(3 LUMINOSITY IN PLANTS. 



function itself can be used as a methodical factor of science of the 

 highest value. 



A demonstration of the importance of oxygen- to luminosity can 

 be made before a large audience in the following way : A glass tul)e 

 closed at one end, having a diameter of about 8 mm. and a length 

 of 1 to 1^- m. is filled to within J to 1 cm. of the top with strongly 

 luminous l)ouillon (bouillon mixed with Bdcter'ntm plioHpliorbrm or 

 Pseiidomonds h/clfcra). Such a tube at the expiration of a quarter 

 of an hour loses its liglit as the bacteria exhaust the oxygen, except 

 the mere upper surface of the liquid in contact with the air. If, now, 

 the tul)e is closed with the thumb and inverted, a bubble of air will 

 ascend through the bouillon, making its entire course luminous and 

 appearing in the darkness like a slowly ascending skyrocket. In a 

 quarter of an hour or less the luminosity again disappears, and the 

 experiment can be repeated. 



Botanists, as a rule, teach that a direct relationship exists in the 

 fungi betw^een the development of light and respiration. Thus 

 Sachs speaks of phosphorescence as the necessary consequence of 

 respiration, of phosphorescence hy means of 7'espiration. But F. 

 Ludwig has already demonstrated that luminous bacteria can be cul- 

 tivated, and therefore made to grow and breathe without any lumi- 

 nosity ; and we can therefore easily see how that at increasing tem- 

 ])eratures the intensity of respiration may steadily increase, but 

 the intensity of luminosity to only a limited degree. The relation 

 existing between light development and oxygen is analogous to 

 that between color development and oxygen. Most of the color- 

 producing bacteria show color only in the presence of oxygen, as 

 can be seen in gelatin cultures into which an infected needle has 

 been introduced. When the free gas can reach the bacteria, the 

 color appears, but deeper in the gelatin the bacteria, cut olf from 

 oxygen, develop without color. Color production and light produc- 

 tion are therefore oxyclation phenomena. *' * * 



During recent time.s quite a number of investigators have been 

 incidentally or directly engaged in throwing light upon the nature 

 of luminosity — E. Pfliiger. liadziszewski, Dubois, F. Ludwig, Katz, 

 Tollhausen, Lehmann. Beijerinck, McKenney, and Nadson. How- 

 ever, their interpretations differ from each other considerably. The 

 further our knowledge of the subject is extended the more probable 

 appears the idea that within the cell is a hypothetical substance, 

 " photogen.'' which has the power of producing light in the presence 

 of free oxygen. This idea receives substantial support from the 

 fact brought out by Kadziszewski that a long list of organic sub- 

 stances, sucli as aldehyde materials, ethereal oils, carbonic-acid, 

 water, fatty oils, and certain of the alcohols, have the power of 

 luminosity when brought into alkaline reaction with active oxygen. 



