184 THE YEAR-BOOK OF AGRICULTURE. 



The growth of a plant presupposes a germ, a seed ; the land-plant requires a soil ; with- 

 out the atmosphere, without moisture, the plant does not grow. The words soil, atmosphere, 

 and moisture are not of themselves conditions ; these are lime, clay, sand-soils, soils origin- 

 ating from granite, from gneiss, from mica-slate, from clay-slate, all entirely different in 

 their compositions and qualities. The word soil is a collective word for a large number of 

 conditions. In a fruitful soil these conditions are combined in proportions adapted to vege- 

 table growth ; in an unproductive soil some of them are wanting. In the same, manner, the 

 words manure and atmosphere include a plurality of terms or conditions. The chemist, with 

 the means at his command, analyzes all kinds of soil ; he analyzes manures, the air, and the 

 water ; he resolves the collective words which express the sum of the conditions of vegetable 

 growth into their single factors, and, in his explanations, substitutes the individual for the 

 combined values. In this process, it is evident there is nothing hypothetical. If it pass for 

 a perfectly-established truth that the soil, the atmosphere, water, and manures exercise a 

 influence upon the growth of the plant, it is no less beyond doubt that this influence is 

 entirely due to the constituents of the soil, &c.; and the province of the chemist is to set 

 these ingredients before the eyes of those occupied with vegetable cultivation, and to illus- 

 trate their qualities and relations. 



1. Plants in general derive their carbon and nitrogen from the atmosphere; carbon in the 

 form of carbonic acid, nitrogen in the form of ammonia. From water (and ammonia) they 

 receive hydrogen. Their sulphur comes from sulphuric acid. 



2. Cultivated in soils, situations, and climates the most various, plants contain a certain 

 number of mineral substances, and, in fact, always the same substances, whose nature is 

 learned from the composition of the ash. These ingredients of the ash were ingredients of 

 the soil. All fruitful soils contain a certain quantity of them. They are absent from no 

 soil in which plants flourish. 



3. In the produce of a field is carried off and removed from the soil the entire quantity 

 of those soil-ingredients which have become constituents of the plant. The soil is richer at 

 seed-time than at harvest. The composition of the soil is changed after the harvest. 



4. After a series of years, and after a corresponding number of harvests, the productive- 

 ness of a field diminishes. When all other conditions remain unchanged, the soil alone 

 becomes different from what it was previously ; the change in its composition is the pro- 

 bable cause of its becoming unproductive. 



5. By means of manures, as stable-dung and animal excrements, the lost fertility may be 

 restored. 



6. Manures consist of decayed vegetable and animal matters, which contain a certain 

 quantity of soil-ingredients. The excrements of animals and of man represent the ashes of 

 food burned in the animal or human body; i.e. the ashes of plants which have been gathered 

 from the soil. In the urine are found those ingredients of the plant, derived from the soil, 

 which are soluble in water ; the solid excrements contain those which are insoluble. Manures 

 contain the materials which the consumed crops have removed from the soil. It is plain that 

 by incorporating manures with the soil the latter receives again the withdrawn ingredients. 

 The restoration of its original composition is accompanied with the recovery of its original 

 fertility. It is certain that one of the conditions of fertility is the presence of certain 

 mineral ingredients in the soil. A rich soil contains more of them than a poor one. 



7. The functions of the roots of plants, in reference to the absorption of atmospheric food, 

 are similar to those of the leaves; i.e. the former, like the latter, possess the property of 

 taking up and assimilating carbonic acid and ammonia. 



8. Ammonia, which is contained in or added to the soil, comports itself as a soil-constitu- 

 ent. The same is equally true of carbonic acid. ' 



9. Animal and vegetable bodies and animal excrements enter into putrefaction and decay. 

 The nitrogen of the nitrogenous matters is thereby converted into ammonia, a small portion 

 of the ammonia decays (oxydizes) further into nitric acid. 



10. We have every reason to believe that nitric acid may replace ammonia in the processes 

 of vegetable nutrition; i.e. that its nitrogen may be applied by the plant to the same pur- 

 poses as that of ammonia. Animal manures accordingly furnish the plant not only with 



