452 A TREATISE ON METAMORPHISM. 



THE AGENTS. 

 PLANTS. 



Chemical work is done by plants both while alive and when dead. 



PLANTS, ALIVE. 



The most important chemical action by the nonbacterial plants is that 

 of the abstraction of carbon dioxide from the atmosphere and its reduction 

 and combination with other elements so as to produce the varices vegetable 

 tissues. The amount of carbon dioxide in the air is exceedingly small, not 

 more than from about 2.76 to 3 volumes in 10,000. Therefore the air in the 

 belt of weathering where plants do not exist can not be presumed to contain 

 more than this proportion of carbon dioxide, except for the very small 

 amount which is brought down by the rain, estimated by Branner in Brazil 

 to be 0.0065 in 1,000 parts by weight." However, by the action of the 

 chlorophyll-bearing plants, which include all of the large and many of the 

 small plants, and by the action of the "red, brown, and blue-green algae," 

 and by one class of bacteria, h carbon dioxide of the atmosphere is reduced 

 and the carbon is concentrated in the plants mainly as cellulose (nC H 10 O 5 ) 

 or woody fiber. This contains 44.4 per cent of carbon. The cellulose 

 produces no marked geological effect so long as the plants are alive; but 

 when dead and acted upon by bacteria, oxygen, and moisture the cellulose 

 furnishes a number of active acids which produce very important geological 

 results. (See pp. 461-465.) 



Plants contain combined nitrogen, but the great majority of plants are 

 unable to obtain their nitrogen from the air; they must use that which is 

 already in a combined state in the soil. A large part of this combined 

 nitrogen is that furnished b)^ the decay of earlier plants and animals. (See 

 pp. 465-466.) But some combined nitrogen is brought to the soil from 

 the air. For instance, in manufacturing, combined nitrogen often escapes 

 in the form of ammonia, and ammonia may also evaporate from the ocean. 

 But this combined nitrogen was derived from earlier plants or animals, and 

 therefore we have as yet no original source for combined nitrogen. 



But it is well known that the nitrogen of the air is to some extent 

 combined with other elements by electric discharge, and thus we have an 



"Branner, J. C, Decomposition of rocks in Brazil, eit. , p. 305. 



i> Fisher, Alfred, The structure and functions of bacteria, translated by A. Coppen Jones, Claren- 

 don Press, Oxford, 1900, p. 107. 



