LECTURE XJV. 



Fungus when not luminous. Again, it has been pointed out, 

 especially by Brefeld, that it is only the young growing hyphae 

 of Rhizomorpha which are luminous. The dependence of the 

 evolution of light upon destructive metabolism is also shewn 

 by the fact that temperature has an influence on luminosity. 

 Fabre states that 3 4 C. is the minimum temperature for 

 the luminosity of Agaricus melleus ; Ludwig found that the 

 luminosity of Rhizomorpha was very feeble at 45 C., and 

 Schmitz observed specimens which were not luminous at 

 17 i8C. Brefeld, however, found Rhizomorpha luminous 

 at a temperature of 12 C. The optimum temperature for 

 the luminosity of Rhizomorpha lies, according to Ludwig, be- 

 tween 25 and 30 C.: at 50 C. its luminosity was permanently 

 destroyed. The curve .of luminosity appears, then, to differ 

 from that of respiration, in that the former begins to fall at a 

 temperature at which the latter continues to- rise. Fabre 

 failed to find that the evolution of light was accompanied by 

 a rise of temperature in Agaricus olearius. 



It is doubtless due to the nature of the light that the 

 luminosity of plants has been termed phosphorescence. Fabre 

 describes the light of Agaricus olearius as being white, soft, 

 and uniform, and compares it to that of phosphorus dissolved 

 in oil. Gardner states that the light of Agaricus, Gardneri 

 has a green tinge, and Rumpf speaks of that of Agaricus 

 igneus as being bluish. According to Ludwig, the light 

 emitted by Rhizomorpha consists of the blue and the more 

 highly refrangible rays. 



We have to attempt, in conclusion, to give, some account 

 of the mode in which the luminosity is produced. In the 

 first place it is not a phenomenon of the same nature as true 

 phosphorescence, for the luminosity of a plant is quite inde- 

 pendent of any previous exposure to the sun, nor can it be 

 induced, as it can in certain substances (phosphorite, chloro- 

 phane) by mere heating. In the second place, it is improb- 

 able, as Pfluger has made clear, that it is due to the formation 

 in the plant of some readily oxidisable phosphorus-compound, 

 such as phosphuretted hydrogen. The immediate disappear- 

 ance of the luminosity on the death of the organism shews 



