254 CHEMISTRY OF PLANT LIFE 



order to utilize other than the parts of the spectrum which are 

 absorbed by chlorophyll and its associated pigments. 



But deep-sea plants show quite a different phenomenon of 

 pigment development. Water is a blue liquid. At depths of 

 40 feet or more, the light which penetrates is devoid of red rays, 

 feeble in yellow, and is characteristically green or blue in color. 

 Now, the red rays of the spectrum are the ones which are most 

 efficient for photosynthesis. Sea weeds which grow at these 

 depths are brilliantly red in color, at intermediate depths they are 

 brown, and at the surface they are green, in the same latitudes. 

 While it is possible that the temperature of the water at these dif- 

 ferent depths may have something to do with the chemical syn- 

 thesis of the pigments, it appears plain that this color change at 

 increasing depths is a definite adaptation to provide for the absorp- 

 tion of the solar energy which is available at these depths. It has 

 been shown that these pigments 'of deep-sea plants are additional 

 to, and not substitutes for, the chlorophylls, etc. The latter pig- 

 merits are present in normal amounts, but are supplemented by 

 those which absorb the green and blue portion of the spectrum. 

 Hence, this type of adaptation might be conceived to be a " sur- 

 vival of the fittest," resulting in the " natural selection " of indi- 

 viduals of the highest total pigmentation. But, on the other hand, 

 there is experimental evidence to show that plants possess some 

 means of varying their pigmentation in response to the character 

 of the light which comes to them. For, it has been found that a 

 complete change in color of certain highly colored plants can be 

 produced in a single generation, by growing the plants in boxes or 

 chambers whose walls are composed entirely of differently colored 

 glass, so that the plants within receive light of only a particular part 

 of the spectrum. In such cases, the plant, starting with an initial 

 " natural " color, changes through a succession of colors until it 

 finally reaches equilibrium at one which provides for the proper 

 absorption of the right kind of light from the new supply which is 

 available to it. Hence, it seems proper to conclude that chromatic 

 adaptation is not a process of " natural selection," but a definite 

 result of an actual mechanism for adaptation to changed environ- 

 mental conditions of supply of radiant energy. 



