EOTATION OF CROPS. 



19 



constantly restoring to the soil a vast 

 amount of those ingredients taken up by 

 the crops, without the aid of man ; but, 

 that these valuable supplies be not 

 wasted, it behoves man to keep the soil 

 in a proper state to receive them. This 

 can only be done by what we have so 

 strongly urged elsewhere — deep cultiva- 

 tion and thin cropping — two important 

 essentials in culture sadly neglected in 

 most gardens, trenching for almost every 

 crop being a thing scarcely tliought of, 

 notwithstanding we are well assured that 

 very much of the success of the London 

 market-gardener, in producing such enor- 

 mous crops, depends on this operation 

 alone. Were half the amount of the 

 value of the manure which is yearly 

 crammed into garden soils expended on 

 trenching, and keeping the surface after- 

 wards open, the advantages would be soon 

 made apparent ; and without that, all 

 the manure, whether special or common, 

 whether mineral or vegetable, and how- 

 ever applied, may be regarded as so much 

 capital thrown away. 



Again, besides the amount of matter 

 restored to the soil, as shown above by M. 

 Barral, an additional supply is returned 

 by the plants themselves, whose leaves are 

 constantly decomposing carbonic acid, 

 which they absorb from the atmosphere, 

 liberating the oxygen, and appropriating 

 the carbon to their own use ; they derive 

 supplies of nitrogen for the formation of 

 their albuminous constituents from the 

 volatile carbonate and nitrate of ammonia, 

 and these they restore to the soil when 

 they are buried in it. From the earliest 

 ages certain crops have been grown for 

 the express purpose of being returned to 

 the soil for its enrichment, a practice pro- 

 bably of more ancient date than that of 

 alchemy, and 3000 years earlier than 

 modern chemistry. The exhaustion of 

 the soil by crops is not so very alarm- 

 ingly great, under good management, 

 as some would have us to believe, and 

 would be much less so if those parts of 

 vegetables that are not to be directly 

 consumed by man were returned to it at 

 the time. Out of a crop of cauliflower, 

 not one-fourth of the bulk of the crop is 

 useable ; hence, if the other three-fourths 

 were immediately dug into the ground 

 on which they were produced, they would 

 return to it veiy nearly as much as they 



had taken from it during their growth, if 

 not more. It is bad management that 

 exhausts a soil ; and one of the worst parts 

 of bad management is taking the whole 

 vegetable produce off the ground, and 

 either not returning it at all, or doing so 

 after it has become so much decomposed 

 and exposed to atmospheric action as to 

 have nearly lost all its fertilising pro- 

 perties. In gai'dens much of this is daily 

 carried on, too many believing that plants 

 derive all their food from the soil. But 

 such is not the case ; the greater part of 

 vegetation is derived from atmospheric 

 sources, and when that is returned to the 

 soil by digging it in, it in this way sup- 

 plies it with more of the organic elements 

 essential to future vegetable growth than 

 the soil contained before the crop was 

 sown or planted ; in other words, it is 

 enriched by the carbon, hydrogen, and 

 nitrogen which the vegetable had ob- 

 tained from sources entirely independent 

 of the soil. 



Plants have the power of converting 

 the materials which constitute both com- 

 mon and special manures by a species of 

 elaboration going on within them, so as 

 to fit and appropriate the necessary quan- 

 tity of each, and to dispose of them 

 throughout the various parts of their 

 structure, leaves, stems, seed, roots, &.C. ; 

 and not only that, but they are capable 

 of supplying themselves at different times, 

 and even in different parts of the same 

 plant, according to their respective natures. 

 " They all form," says Professor John- 

 ston (in " Experimental Agriculture," p. 

 9), "more or less constantly and abun- 

 dantly, a portion of the fixed and solid 

 matter of the plant taken as a whole. 

 They may not be found in any one part 

 of the plant, when separated carefully 

 from the rest, but, in the solid parts of 

 the plant, taken as a whole, they are all, 

 and always to be met with. When thus 

 deposited, they become for the most part 

 dormant, as it were, and for the time 

 cease to perform active chemical func- 

 tions in the general growth, though, as 

 vessels or cells, they may still perform 

 a mechanical function. They undergo 

 various chemical changes in the inter- 

 course, chiefly while circulating or con- 

 tained in the sap, by which changes they 

 are prepared and fitted for entering, when 

 and where it is necessary, into the solid 



