VEGETATION AND THE ATMOSPHERE 45 



all the ingenious means and powerful drugs they 

 possess to extract carbon from carbonic acid gas. 

 This task, which would tax the utmost resources of 

 the man of science, leaves accomplish noiselessly, 

 without effort, even instantaneously, and with the 

 sole requirement that they shall have the aid of the 

 sun. 



"But if sunlight fails, the plant can do nothing 

 with the carbonic acid gas, the chief item in its diet. 

 It then pines away with hunger, shoots up as if in 

 quest of the missing sunshine, while its bark and 

 leaves turn pale and lose their green color. Finally 

 it dies. This sickly state induced by the absence of 

 light is called etiolation. It is artificially produced 

 in gardening for the purpose of obtaining tenderer 

 vegetables and of lessening or even entirely remov- 

 ing the too strong and unpleasant taste of some 

 plants. In this way some salad greens are bound 

 with a rush so that the heart, deprived of the sun's 

 rays, may become tender and white ; and thus, too, 

 celery is banked up and left to whiten, since other- 

 wise its taste would be unbearable. If we cover 

 grass with a tile or hide a plant under a pot turned 

 upside down, we shall after a few days of this en- 

 forced darkness find the foliage all sickly and yellow. 



"When, on the other hand, the plant receives the 

 sun's rays without hindrance, the carbonic acid gas 

 is decomposed in no time, the carbon and the air 

 separate, and each resumes its original properties. 

 Freed of its carbon, the air becomes what it was be- 

 fore this admixture : it becomes pure air, fit to main- 



