COLOR 



175 



phyll only in sunlight, though several instan- 

 ces are known in which the green color is to 

 be found in tissues in complete darkness. The 

 presence of iron in the cell is necessary for the 

 formation of chlorophyll, although it does 

 not enter into the composition of the pigment. 



When a plant is grown in complete darkness 

 it assumes a pale waxy yellow color, the or- 

 gans are usually abnormal in size and form, 

 and are said tohe etiolated. The yellow color 

 of etiolated plants is etiolin which resembles 

 chlorophyll in general chemical composition 

 and ph^^sical properties. Many writers be- 

 lieve that etiolin is formed in the earlier stages 

 of the construction of the chlorophyll mole- 

 cules. In support of this view it has been no- 

 ticed that plants grown in darkness and con- 

 taining large quantities of etiolin turn green 

 on exposure to light much more rapidly than 

 those in which but little etiolin was found. 

 Etiolin is not to be confused with the yellow 

 colors of fruits and flowers, which are due to 

 an entirely different class of pigments next to 

 be considered. 



The lipochromes are a series of substances 

 varying through yellow and red, devoid of 

 nitrogen, and which absorb certain blue violet 

 rays of sunlight. These substances occur in 

 company with chlorophyll in leaves and else- 

 where in bacteria, algae, fungi, as well as in 



Etiolin 



The lipo- 

 chromes 



