POTASH AND SODA PREPARE THE FOOD OF PLANTS. 329 



where they naturally abound, or are artificially supplied, the crops will 

 as certainly ])rove both more early and more abundant — provided no 

 other essential food be deficient in the soil. 



In reference to this mode of action i.; will occur to you that potash is 

 the more likely of the two to be beneficial to our cultivated crops, inas- 

 much as the ash of those plants which are raised for food is generally 

 much more rich in potash than in soda. [Seethe tabular details given in 

 Lecture X., § 3., p. 216 et seq.'] But this may possibly arise from the 

 more abundant presence of potash in the soil generally, since some 

 chemists are of opinion that soda may take the place of potash in the in- 

 terior of plants, without materially affecting their growth, [Berzelius 

 Chimie, VI., p. 733, edit. 1832.] This hypothesis, whatever may be 

 its theoretical value, will prove useful to practical agriculture if it lead to 

 experiments from which the relative action of each of these carbonates, 

 in tlie same circumstances, may be deduced, — and the specific influ- 

 ence of each, in promoting the growth of particular plants, in some de- 

 gree determined. Potash (or wood-ashes) aids the growth of corn after 

 turnips or potatoes (Lampadius) — would soda do the same ? Carbon- 

 ate of soda assists in a remarkable manner the growth of buck-wheat 

 (Sprengel) — wouldthe same good effects follow from the use of potash ? 



h. Another purpose which these carbonates are supposed to serve, is 

 that of combining with, and rendering soluble, the vegetable matter of 

 the soil, so as to bring it into a state in which it may be readily con- 

 veyed into the roots of plants. They may in this case be said to pre- 

 pare the food of plants. That they are really capable of forming 

 readily soluble compounds with the humic acid, and with certain other 

 organic substances which exist in the soil, is certain. Those, however, 

 who maintain with Liebig that plants imbibe all their carbon in the 

 form of carbonic acid, will not be willing to admit that this property of 

 the above carbonates can either render them useful to vegetation, or ac- 

 count for the beneficial action they have so often been observed to exer- 

 cise. From this opinion we have already seen reason (pp. 63 and 64,) 

 to dissent, and we are prepared, therefore, to concede that potash and 

 soda, in the form of carbonates, may act beneficially upon vegetation — 

 by preparing the organic matter of the soil for entering into the roots of 

 j)Iants, and thus administering to their growth. 



This preparation also may be effected either by their directly com- 

 bining with the organic matter, as they are known to do with the humic 

 and other acids which exist in the soil ; or by their disposing this or- 

 ganic matter, at the expense of the air and of moisture, to form new 

 chemical compounds whicli shall be capable of entering into the vege- 

 table circulation. This disposing influence of the alkalies, and even of 

 lime, is familiar to chemists under many other circumstances. 



This mode of action of the carbonates of potash and soda can be ex 

 ercised in its fullest extent only where vegetable matter abounds in the 

 soil. It is stated by Sprengel [Lehre vom Diinger, p. 402,] according- 

 ly, ^s the result of experiment, that they are most useful where vegeta- 

 ble matter is plentiful, and that they ought to be employed more spar- 

 ingly, and with some degree of hesitation, where such organic matter is 

 deficient. 



c. We have already seen, during our study of the composition of the 



