DEVELOPMENT OF LIGHT AND HEAT. 503 



and ultimately entirely vanishes, although apparently the relations and conditions 

 of life are exactly the same as before. I have repeatedly taken up luminous wood 

 at night, and having brought it home, have tried to reproduce as far as possible 

 the conditions under which the luminosity existed in the open; in the first night 

 the light was unweakened, but after twenty-four hours it had usually disappeared 

 entirely. If the luminous wood is placed in a closed space where the renewal of 

 the air, i.e. of oxygen, is not carried on to a suflficient extent, the luminosity soon 

 ceases. A rise of temperature is not favourable to its continuance, principally from 

 the fact that a higher temperature brings about an alteration in the hygrometric 

 condition of the wood. In pure oxygen the wood shows a decrease rather than an 

 increase of light. In the depths of the forest the luminosity may be observed day 

 after day for more than a week on the same trunk, if the conditions of humidity 

 remain the same. 



It is difficult to compare the light emitted from the mycelium with any other. 

 It is not so green as that of glowworms, and has not the brilliancy of the phos- 

 phorescence of the sea; it is a dull white light. It most resembles that of pure phos- 

 phorus held under water. In the gloom of the forest it has a strange and therefore 

 uncanny appearance, and the " will-o'-the-wisp " may, in part at any rate, be attri- 

 buted to luminous wood. If a decayed tree-trunk penetrated by the light-giving 

 mycelium is vigorously struck, so as to split it into hundreds of fragments, which 

 fly out in all directions and fall scattered on the ground, each spKnter becomes 

 luminous, and the dark forest ground seems to be strewn with dots of light. The 

 luminosity of these fragments, however, comes to an end before the next night. 



The Rhizomorph and other allied agarics only exhibit the luminosity in their 

 mycelium, their fructifications remaining dark under all circumstances. In a series 

 of other agarics, viz. in the Brazilian Agaricus Gardneri, in Agaricus igneus, a 

 native of Amboina, in Agaricus noctilucens, living in Manila, and in Agaricus olear- 

 ius, which is widely distributed through the Mediterranean floral district, the actual 

 fructifications emit light, usually from the hymenium developed on the under side 

 of the cap, but more rarely the stipe also which bears the cap. The light produced 

 by these fungi is like that from the mycelium of the agarics described previously, 

 and the external conditions under which it occurs are also similar, except that the 

 hygrometric state has not such a noticeable efiect on it as on the luminous wood 

 permeated by mycelial threads. At least in Agaricus olearius, a mushroom which 

 grows among the roots of olive trees and forms its golden-yellow fructification in 

 late autumn, the luminosity is to be seen equally well in dry and wet weather. As 

 soon as the temperature falls below -f 3°, the light immediately ceases; it is best at 

 8-10°, and under higher temperatures it does not increase but gradually diminishes. 

 If oxygen be kept away or withdrawn from the air, the luminosity immediately 

 vanishes, but as soon as the atmospheric air is again restored, the phenomenon 

 reappears. Dying agarics become less and less luminous, and their light is ex- 

 tinguished at their death. It is to be noted that not only agarics with luminous 

 hymenia, but also those with luminous mycelia, emit light both by day and night. 



