i6 COLOUR IN NATURE chap. 



are already familiar to most people. It is more to 

 our purpose to note the organisms among which 

 it occurs, and the special parts with which it is 

 associated. 



To begin with the simplest organisms— the fact 

 that many decaying substances shine in the dark 

 has long been known, and modern bacteriologists 

 have been able to isolate the specific micro-organisms 

 which possess, under certain conditions, this property 

 of evolving light. Just as in the case of pigment 

 production, so also the phosphorescence depends upon 

 the nature of the organism and the character of its 

 surroundings. Thus Photo-bacterium pkosphorescens 

 evolves light during the fermentation of sugar if free 

 oxygen be present and the temperature be favour- 

 able (3^-35^ C). 



Among the Protozoa, phosphorescent forms are 

 most noticeably represented by the genus Noctiluca, 

 but some Radiolarians, such as Thalassicola, are also 

 luminous. In Noctiluca the phosphorescence is said 

 by Allman to be produced in the cortical layer of 

 protoplasm. 



Among multicellular plants phosphorescence is 

 apparently confined to the fungi. It is an old 

 controversy whether it does or does not occur in 

 flowering plants, but most authorities answer the 

 question in the negative. In the fungi the 

 luminosity is marked in several species of Agaricus. 

 The phenomenon is only manifest in the presence of 

 free oxygen, is associated with oxidative processes, 

 and is dependent upon the temperature. The light 

 is said to be usually of blue or greenish colour, but 

 in some cases is quite white. 



