ASSIMILATION OF CARBON. 



17 



tion which is mucn under the truth in the 

 case of woods, meadows, and corn fields ; 

 and if we farther suppose that carbonic acid 

 equal to 0.00067 of the volume of the air, 

 or 1-1 000th of its weight is abstracted from 

 it during every second of time, for eight 

 hours daily, by a field of 53,814 square feet 

 (== 2 Hessian acres ;) then those leaves 

 would receive 1102 Ibs. of carbon in two 

 aundred days.* 



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 independent of solar 

 light. During the day, when the 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 colour 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 cloud- 

 ed, permits the glowing rays of the sun to 

 shine upon an immeasurably luxuriant ve- 

 getation. The temperate and cold zones, 

 where artificial warmth must replace defi- 

 cient heat of the sun, produce, on the con- 

 trary, carbonic acid in superabundance, 

 which is expended in the nutrition 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 car- 

 bonic acid formed during our winter. 



The experiments of De Saussure have 



* The quantity of carbonic acid which can be ex- 

 tracted from the air in a given time, is shown by 

 the following calculation. During the whitewash- 

 ing of a small chamber, the superficies of the 

 walls and roof of which we will suppose to be 105 

 square metres, and which receives six coats of 

 lime in four days, carbonic acid is abstracted from 

 the air, and the lime is consequently converted, 

 on the surface, into a carbonate. It has been ac- 

 curately determined that one square decimetre re- 

 ceives in this way, a coating of carbonate of lime 

 which weighs 0.732 grammes. Upon the 105 

 square metres already mentioned there must ac- 

 cordingly He formed 7686 grammes of carbonate 

 of lime, which contain 4325.6 grammes of carbo- 

 nic acid. The weight of one cubic decimetre of 

 carbonic acid being calculated at two grammes, 

 (more accurately 1.97973.) the above mentioned 

 surface must absorb in four days 2.163 cubic me- 

 tres of carbonic acid. 2500 square metres (one 

 Hessian acre) would absorb, under a similar treat- 

 ment, 51 i cubic metres=1818 cubic feet of car- 

 bonic acid in four days. In 200 days it would ab- 

 sorb 2575 cubic metres= 904,401 cubic feet, which 

 contain 11,353 Ibs. of carbonic acid, of which 3304 

 Ibs. are carbon, a quantity three times as great as 

 that which is assimilated by the leaves and roots 

 growing upon the same space. 



proved, that the upper strata of the air con- 

 tain more carbonic acid than the lower, 

 which are in contact with plants ; and that 

 the quantity is greater by night than by day, 

 when it undergoes decomposition. 



Plants thus improve the air by the remo- 

 val of carbonic acid, and by the renewal of 

 oxygen, which is immediately applied to 

 the use of man and animals. The horizon- 

 tal currents of the atmosphere bring with 

 them as much as they carry away, and the 

 interchange of air between the upper and 

 lower strata, which their difference of tem- 

 perature causes, is extremely trifling when 

 compared with the horizontal movements 

 of the winds. Thus vegetable culture 

 heightens the healthy state of a country, 

 and a previously healthy country would be 

 rendered quite uninhabitable by the cessa- 

 tion of all cultivation. 



The various layers of wood and mineral 

 coal, as well as peat, form the remains of a 

 primeval vegetation. The carbon which 

 they contain must have been originally in 

 the atmosphere as carbonic acid in which 

 form it was assimilated by the plants which 

 constitute these formations. It follows from 

 this, that the atmosphere must be richer in 

 oxygen at the present time than in former 

 periods of the earth's history. The increase 

 must be exactly proportional to the quantity 

 of carbon and hydrogen contained in these 

 carboniferous deposits. Thus, during the 

 formation of 353 cubic feet of Newcastle 

 splint coal, the atmosphere must have re 

 ceived 643 cubic feet of oxygen produced 

 from the carbonic acid assimilated, and also 

 158 cubic feet of the same gas resulting 

 from the decomposition of water. In for 

 mer ages, therefore, the atmosphere must 

 have contained less oxygen, but a much 

 larger proportion of carbonic acid, than it 

 does at the present time, a circumstance 

 which accounts for the richness and luxuri- 

 ance of the earlier vegetation. 



But a certain period must have arrived in 

 which the quantity of carbonic acid con- 

 tained in the air experienced neither increase 

 lor diminution in any appreciable quantity. 

 For if it received an additional quantity to 

 ts usual proportion, an increased vegetation 

 would be the natural consequence, and the 

 excess would thus be speedily removed. 

 And, on the other hand, if the gas was less 

 than the normal quantity, the progress 

 of vegetation would be retarded, and the 

 proportion would soon attain its proper 

 standard. 



The most important function in the life 

 of plants, or, in other words, in their as- 

 similation of carbon, is the separation, we 

 might almost say the generation^, of oxygen, 



matter can oe considered as nutritious, 

 or as necessary to the growth of plants, 

 which possesses a composition either simi- 

 ar to or identical with theirs, and the as- 

 similation of which, therefore, could take 

 alace without exercising this function. The 

 reverse is the case in the nutrition of ani 



