Luminous Moss. 37 



were wending from west to east, which was their 

 proper course." 



By the botanists this luminous moss is placed 

 in a genus called Schizostega or Schistostega. If it be 

 true that it is only to be looked for in damp caves 

 or on exposed moors when the air is in an electrical 

 condition, it will seldom be sought except by the 

 zealous specialist. 



The explanation of this curious light, given in the 

 " Class Book of Botany," by J. H. Balfour, agrees 

 very well with the use which Major Vaughan is said 

 to have made of it, as indicating the points of the 

 compass, although one might suppose that the shim- 

 mering gleam of the departed sun, which lighted up 

 the moss, would have been as good a guide. " The 

 light," it is said, "given out by some mosses, as 

 Schistostega osmundacea and Mnium punctatum, 

 depends on optical appearances, and has nothing to 

 do with the development of light from the substance 

 of the plants. In the former, the cellules of the ger- 

 minating plant swollen into little globules, and in 

 the latter the small drops of water on the leaves, 

 produce a glimmering by a peculiar refraction and 

 reflection of the daylight. The light of Schistostega 

 is a delicate emerald green." * 



On another occasion David was the victim of a 

 rather more perilous luminosity. This incident he 

 describes as follows : 



" Having to start for coals by three in the morning, 

 and having been early up the morning before, I was 

 afraid of sleeping in, and thought it best, instead 



* "Class Book of Botany," third edition, 1870, p. 675. 



