LUMINOSITY IN PLANTS. 853 



The cause of this light dovelopment, Bacterium, phosplioreum^ is 

 one of the most widely distributed of the bacteria. It is found on 

 meat in refrigerators, in slaughterhouses, in butcher shops; in fact, 

 it finds an entrance into our kitchens where meat is usually prepared. 

 For in no other w^ay can we explain the fact that so many specimens 

 of meat display the power of spontaneous luminosity. I have of late 

 come upon another form of light production, which, although of com- 

 mon occurrence, is practically unknown. I refer to light from decay- 

 ing leaves. During walks taken at night in the Trojjics, especially 

 in Java, I frequently found the dead leaves of Bamhusa^ N ef helium^ 

 Aglaia^ and other plants to be luminous in the darkness. On return- 

 ing to Europe w-ith the experiences gathered in the Tropics, I looked 

 into the same subject on native ground and found that luminous 

 dead leaves of the oak and beech are quite common in middle Europe. 

 The leaves must be in a somewhat moist condition and to some extent 

 decayed. Such leaves, especially, as display on account of decay a 

 somewdiat yellowish or ashen color or show^ spots of yellow and 

 brown give a particularly beautiful light. The luminosity is usually 

 local, rarely over the entire surface — a white, soft, steady light. 

 Here also the luminous cause is not the leaf substance, but the living 

 fungus within it. 



According to my own observations, no inconsiderable percentage of 

 fallen oak and beech leaves are luminous in the summer time; and on 

 all sides the floor of the forest is illuminated with light, feeble, indeed, 

 but easily detected. Unfortunately I have not as yet been able to 

 isolate the fungus which produces this light of decaying foliage. 

 Still I have employed wath advantage the methods of pure cultures 

 with the fungus, producing light in wood, and thereby have recog- 

 nized in Agar'icus melleus and Mycelium x the two fungi which 

 Avith us most frequently cause this luminosity. At the same time it 

 has become evident that certain cryptogams generally considered 

 as luminous fungi, such as Xylaria Ilypoxylon^ must be stricken out 

 of the list of the Photomycetes, and to this may also be added Tra- 

 'tnetes pini. 



In Bacterium p/wsphoreimi (Cohn), Molisch and Mycelium "x" 

 (necessarily so called at present, as despite years of cultivation it has 

 not yet fruited), are secured two remarkably valuable experimental 

 adjuncts for accurately studying light development in a definite way, 

 because of their relatively powerful intensity of light and the un- 

 usually long period that they are luminous. 



Luminosity and the growth of luminous bacteria are dependent, 

 among other things, upon certain salts and organic substances. Table 

 salt plays a prominent part in this respect, seeing that as a rule these 

 bacteria are marine, and for this reason 3 per cent of table salt is 

 generally added to the culture medium. The salt does not serve as 



