292 PHYSIOLOGY OF NUTRITION. 



must of course be determined by special preliminary examina- 

 tion. 



In our figure, the dead shoot d is fastened by a thread to the 

 support s, while the living shoot stands in the vessel of water a\ 

 To secure the provision of air saturated with moisture, the plants 

 are placed in the flower-pot, a, the rim of which supports a sheet 

 of plaster of Paris, on which rests a bell-glass provided round 

 the bottom with moist sand. 



In employing the above method, more attention must be paid 

 than hitherto has been to the possibility that electric currents are 

 set up merely in consequence of the contact of the thermo-electric 

 junctions with the moist plant structures. 



That some plants emit light in consequence of their vital pro- 

 cesses is a demonstrated fact. Thus there are, e.g., a series of 

 phosphorescent bacteria, and I myself once was able to observe the 

 phosphorescence, due to bacteria, emitted from putrid fish. 



Similarly the phosphorescence of Agaric us olearius, A. melleus, 

 and Xylaria hypoxylon is well known. The phenomena in question 

 have been studied especially by Fabre and Ludwig in Greiz. 

 Agaricus melleus grows chiefly on conifers, and if in winter we dig 

 up the roots of the trees attacked, or collect portions of the sticks 

 containing its mycelium, we can easily observe in the dark the 

 light emitted by the wood, especially if the material has 

 previously been kept for a day in a damp cellar. If we note the 

 trees or sticks infected by the Agaricus, we can at any time of 

 the year procure luminous wood. 



The above-mentioned species of Xylaria is to be found through- 

 out the year on beech sticks. The infected wood shines with a 

 greenish yellow light. The light emitted by " luminous wood " 

 penetrated by Agaricus melleus appears, on the contrary, whitish 

 with a tinge of green. 



If luminous wood is immersed for a short time in water at 80- 

 100 C., it loses its power of shining in the dark, since the fungus 

 has been killed by the heat. The luminosity of the wood is also 

 arrested in absence of Oxygen, e.g. in a stream of Hydrogen, but 

 is resumed on exposure to the air. The luminosity is due to a 

 process of oxidation, which is dependent, in a manner still not 

 understood, on the vitality of protoplasm. 



1 See G. Kraus, Abhandlunyen d. naturforsch. GesellscJiaft zu Halle, Bd. 16, 

 In this paper also the literature is collected. 



