Animal Luminescence 105 



achieves. The heather is a dual organism ; it is like a 

 flowering lichen! If it stood alone it would be a re- 

 markable curiosity, but it is only an instance of a 

 kind of partnership that is now known to be common, 

 between the highest plants and the lowest. The list 

 of flowering plants with fungi (mycorhiza) living in 

 profitable partnership with their roots is already a 

 long one. The root-tubercles of Leguminosae, due to 

 nests of symbiotic Bacteria, are familiar, and of con- 

 siderable importance in agriculture. Familiar, we 

 say, but it does not seem at all clear as yet how it is 

 that the partnership enables the quiet-living plant to 

 capture the nitrogen of the air — a feat which man 

 accomplishes by harnessing waterfalls to electric 

 machines and sending terrific lightning discharges 

 through the air. 



Considerable progress has been made with the 

 physiology of animal luminescence. Indeed, the 

 chemistry of the transformation of energy has out- 

 run our knowledge of what the light means in the life 

 of the creature. The gleams, so badly called "phos- 

 phorescent," may be lanterns, or lures, or danger- 

 signals, or love-lights, or recognition-marks, or what- 

 not — speculation is rife because ecological observa- 

 tions and experiments have been few. As to the 

 physiology, however, it seems to have been well estab- 

 lished in the case of the firefly, the crustacean Cypri- 

 dina, and the rock-boring bivalve, the piddock or 

 Pholas, that a ferment-like substance, luciferase, acts 

 on an oxidizable substance, luciferin, changing chemi- 

 cal energy into light. Our point, in connection with 



