Radiant Energy 89 



mucous coating on many littoral algae, snails, and fishes helps 

 such organisms to resist desiccation. 



Radiant Energy 



Radiant energy exerts profound influences on organisms. It 

 produces chemical changes which are injurious to protoplasm; 

 stimulates or inhibits the activity of protoplasm or of whole organ- 

 isms; makes possible the perception of distant objects by vision; 

 stimulates formation of pigment, colors, and patterns; activates 

 substances in organisms and foods so that they acquire greater 

 value for nutrition and metabolism; stimulates the activity of 

 endocrine glands; energizes photosynthesis; etc. Laurens (1928) 

 points out that light is risible radiant energy and that it is a mis- 

 nomer to speak of ultra-violet or infra-red light. A man perceives 

 radiant energy as light which has ranges between 390l^'l^ and VSOV^V-; 

 a honey bee has a range which extends further into the shorter 

 vibrations. The vibrations which are most effective in causing 

 pigment formation in man are about BOO^J-l^ in length; still shorter 

 vibrations cause sunburn. 



Radiant energy is absorbed in a selective manner as it passes 

 through water. In a general way the longer wavelengths are 

 eliminated near the surface, and the shorter vibrations penetrate 

 deepest. Penetration may be interfered with by suspended matter, 

 surface disturbances, stains, and other things. Seas are usually 

 clearer than rivers and lakes. In a lumber region the presence of 

 tannin in water cut down the blue light that would normally 

 reach to considerable depths (Shelf ord, 1929) . 



Organisms from the ocean may, if they become established on 

 land, gain certain advantages because more radiant energy is avail- 

 able for the manufacture of foods and the furthering of metabolic 

 processes, but they may also suffer from the injurious effects that 

 such energy often produces. In general plants and animals are more 

 or less precisely adjusted to carry on their daily activities in certain 



