296 Afp'icultural Chemistry. 



root-fibres, of the same size (p. 32). When all the conditions 

 indispensable to the conversion of carbonic acid into a constituent 

 of the plant, and which must be derived from the soil, are 

 present in sufficient quantity and in available forms, then only so 

 much carbonic acid can be fixed or condensed as is presented 

 to its organs of absorption by the surrounding media (p. 196). 

 Without a simultaneous supply of ammonia, the plant does not 

 attain its full development (p. 187). 



But if to the roots and leaves of the young plant there be 

 supplied, in the same time, three times as much carbonic acid as 

 the air contains, there will be formed, in the same time, four 

 times as many roots, leaves, and buds. The surface, and with it 

 the power of the plants to take up food from the air through the 

 leaves, will be increased fourfold beyond what it would have been 

 without this additional supply (p. 196). The plant will take 

 up more mineral food, in diiect proportion to the increase of its 

 mass derived from the soil. The number and size of the seeds 

 will depend on the quantity of mineral elements of nutrition which 

 the soil has yielded to the plant in the same time (p. 197). 

 The effect of the carbonic acid artificially supplied, as well as 

 that of the ammonia (p. 211) consists, therefore, in the gaining 

 of time (p. 199). 



The increase in the produce of a field depends, on the whole, in 

 cultivation on the great scale, according to the preceding explanation, 

 on this : that while we provide in the soil, at the favourable time, 

 a source of carbonic acid and ammonia, the absorbing surface of the 

 field is increased, both upwards and downwards, by these nutri- 

 tive materials. A double surface of leaves must come in contact 

 with twice as many particles of air, and must take up, in the same 

 time, twice as much carbonic acid. The air, in the same time, 

 is more completely deprived of its carbonic acid.* A double 

 number of root-fibres receives twice as much of the terrestrial 

 elements of nutrition from the soil. By the mechanical prepara- 

 tion of the soil we remove the obstacles which impede the 



* Mr. Lawes, obviously under the impression, as it appears to me, that my 

 explanation is quite new, and not aware that it is to be found, verbatim, in my 

 book, since 1843, has made the following remarks on it (Journal, vol. xvi. p. 453 j. 

 " What, we -would ask again, is gain of time, in the growth of plants, but the very 

 essence of the distinction between natural growth and artificial growth, that is, 

 agriculture ? In this admission is involved the fullest and most convincing proof 

 that, if any of the constituents of plants should have attributed to them a pt'cpo7i- 

 deratiiyj value and importance, it should be those to which is due a gain of time." 



I can only rejoice that Mr. Lawes has now recognized the significance of my 

 explanation. When, five years ago. Dr. Daubeny directed his, Mr. Lawes', atten- 

 tion to it, he clearly did not understand it (Journal, i. 40) ; but my little pamphlet 

 ('Principles of Agricultural Chemistry') appears to have opened his eyes. It 

 is self-evident that science knows nothing of a preponderating value of any one 

 element of nutrition. Each of them has, under certain circumstances, a value or 

 importance beyond the others. 



