46 OF THE ASSIMILATION OF CARBON. 



But it is inconceivable, that the functions of the 

 organs- of a plant can cease for any one moment 

 during its life. The roots and other parts of it, 

 which possess the same power, absorb constantly 

 water and carbonic acid. This power is independ- 

 ent of solar light. During the day, when plants are 

 in the shade, and during the night, carbonic acid is 

 accumulated in all parts of their structure ; and the 

 assimilation of the carbon and the exhalation of 

 oxygen commence from the instant that the rays of 

 the sun strike them. As soon as a young plant 

 breaks through the surface of the ground, it begins 

 to acquire color from the top downwards ; and the 

 true formation of woody tissue commences at the 

 same time.* 



The proper, constant, and inexhaustible sources 

 of oxygen gas are the tropics and warm climates, 

 where a sky, seldom clouded, permits the glowing 

 rays of the sun to shine upon an immeasurably 

 luxuriant vegetation. The temperate and cold zones, 

 where artificial warmth must replace deficient heat 

 of the sun, produce, on the contrary, carbonic acid 

 in superabundance, which is expended in the nutri- 

 tion of the tropical plants. The same stream of 

 air, which moves by the revolution of the earth from 

 the equator to the poles, brings to us, in its passage 

 from the equator, the oxygen generated there, and 

 carries away the carbonic acid formed during our 

 winter. 



accordingly be formed 7686 grammes of carbonate of lime, which con- 

 tain 4325-6 grammes of carbonic acid. The weight of one cubic deci- 

 metre of carbonic acid being calculated at two grammes, (more accu- 

 rately 1-97978,) the above-mentioned surface must absorb in four days 

 2-163 cubic metres of carbonic acid. 2500 square metres (one Hessian 

 acre) would absorb, under a similar treatment, 51^ cubic metres = 1818 

 cubic feet of carbonic acid in four days. In 200 days it would absorb 

 2575 cubic metres = 904,401 cubic feet, which contain 11,353 lbs. of 

 carbonic acid, of which 3304 lbs. are carbon, a quantity three times as 

 great as that which is assimilated by the leaves and roots growing upon 

 the same space. — L. 



* Plants that grow in the dark, are well known to be colorless. This 

 is seen in the blanching of celery (etiolation), the earth is heaped 

 around the stalks to exclude the light. 



