SUPPLY OP ORGANIC PARTS TO PLANTS. 247 



plied from the air and water in any quantities required in propor- 

 tion to the amount of carbon and azote derived from all sources. 

 Chemists seem to concur in the opinion that plants exert the power 

 to decompose water received through their roots into their sap 

 vessels, and to assimilate the results of the decomposition, hydro- 

 gen and oxygen, in requisite proportions. Besides all other reasons 

 in support of this opinion, its truth may be inferred from the 

 established fact that in many vegetable substances the constituents 

 of hydrogen and oxygen are present in precisely the proportions 

 which serve to constitute water. 



If then enough azote and carbon be furnished to growing plants, 

 enough of oxygen and hydrogen will be at the same time taken up 

 and assimilated, by the plant's own natural powers. 



The foregoing views seem to offer the only plausible explanation 

 of that great mystery of vegetable life, that plants on barren land 

 should pine or starve, when surrounded by unlimited supplies, in 

 air and water, of their necessary elements. 



The supply of azote to the roots must be limited to the amount 

 of azotized matters already in the soil, and to such subsequent 

 additions as can be furnished in prepared putrescent manures, or 

 in the azotized green or dry products of the land left there to de- 

 cay. If we could also increase the supply of carbonic acid in the 

 atmosphere, the benefit to plants would be as great as the giving 

 of azote in manure. It has been proved by experiments, that of 

 different plants kept in confined artificially composed atmospheres, 

 those grew best, which had carbonic acid in much larger propor- 

 tion than is in the natural atmosphere. (Boussingault, p. 36.) 

 To increase the quantity of carbonic acid diffused through the 

 atmosphere, to any useful or even appreciable extent, is beyond the 

 power of man. But the desired results of such increase would be 

 reached in some measure by enabling plants to inhale and assimi- 

 late more than their share of the general supply of carbonic acid 

 in the whole atmosphere. This is partially effected for all vegeta- 

 ble growth by the winds, which continually renew the air in con- 



most other late and high authorities, supposes the carbon of plants to be 

 derived principally from the atmosphere, and through the leaves, but also 

 in part from the earth and through the roots. Liebig asserts that carbon 

 is furnished altogether through the leaves, except during germination ; and 

 none through the roots, after the opening of the earliest leaves from the 

 seed. This opinion seems to involve the absurd position that the carbona- 

 ceous (dark-coloured) part of manure, usually deemed evidence of richness 

 in manure and in soil, is of no use to plants through their roots ; nor 

 otherwise, except to furnish more carbonic acid to the atmosphere. In this 

 event, the manure, by its carbonaceous part, may possibly assist the 

 growth (through the leaves) of the plants growing nearest. But if any 

 wind was blowing when the gas rose from the earth, the manure would be 

 as likely to take effect on distant as on the nearest plants, even if not car- 

 ried out of reach of all for the time being. 



