THE DESCENDING SAP 



137 



or less remotely with respiration i.e. with 

 the combustion of carbon compounds in 

 living cells. Many theories, however, 

 have been advanced to account for the 

 phenomena of luminosity, and the paucity 

 of our knowledge on the subject may be 

 gathered from the fact that the very 

 existence of the phenomena at least, 

 in the higher plants is to this day gravely 

 questioned by many botanists. In our 

 opinion the evidence in favour of the 

 alleged occurrences is too accumulative 

 to be resisted ; though doubtless they are 

 due to other causes than those which pro- 

 duce the phosphorescence in plants of 

 lower organization, as we hope presently 

 to show. 



The great naturalist Linnaeus was the 

 first at least in modern times to record 

 an observation on the subject, his atten- 

 tion having been drawn to it by his 

 daughter, Christina Linne. Walking in 

 her father's garden one hot June evening, 

 she observed the flowers of Tropceolum 

 majus (the Garden Nasturtium) give forth 

 sparks or flashes. The phenomenon was 

 repeated on successive evenings, and also 

 in the mornings before sunrise, when 

 not only her father, but other men of 

 science were present. One of these gentle- 

 men, a well-known electrician named 

 Wilcke, believed the flashes to be electric ; 

 and this appears to be the opinion of 

 most writers who have investigated the 

 subject since ; though some believe that 

 the scintillations are only apparent, and 

 class them among optical illusions. The 

 fact that the flashes are invariably ob- 

 served at times when the air is dry and 

 charged with electricity, is, however, ail 

 argument and a pretty strong one in 

 favour of the former view. 



Perhaps no flowers exhibit this phenomenon in a more remarkable 

 degree than those of the plant noticed by Linnaeus ; though the common 



Photo by] ' IE. Step. 



FIG. 173. MARTAGON LILY (Lilium 

 martagon). 



One of the plants whose flowers are said to be 

 luminous. EUROPE, ASIA 



