ROTATION OF CROPS. 



21 



doubt they answer a purpose analogous 

 to the bones in animals, formed of lime, 

 which is a mineral substance also. 



Although, however, the presence of 

 mineral substances in plants is neces- 

 sary, yet they do not in general abound in 

 large quantities. Their presence is not 

 the result of accident, but of wise design, 

 as beautifully shown by Professor Lin- 

 dley in "Theory of Horticulture," p. 356 

 — " For although it may be asserted that 

 the presence of iron, copper, or other sub- 

 stances, in plants, in minute quantities, is 

 accidental and unimportant, yet such a 

 supposition is gratuitous, if not altogether 

 unfounded ; for I do not know what war- 

 rant we have for saying that any of the 

 constant phenomena of nature, however 

 minute they may seem to be, are acci- 

 dental. This at least is certain, that 

 where mineral substances occur abun- 

 dantly in plants, they are part and parcel 

 of their nature, just as much as iron and 

 phosphate of lime are of our own bodies ; 

 and we must no more suppose that grasses 

 can dispense with silica in their food, or 

 marine plants with common salt, than 

 that we ourselves could dispense with 

 vegetable and animal food. 



" Flint is found on the exterior of the 

 whole graminaceous order without excep- 

 tion. It forms the polished surface of 

 the cane palm, the grittiness of many 

 kinds of timber. Sulphur abounds in 

 cruciferous plants, especially mustard ; 

 copper in coffee, wheat, and many other 

 plants, (it is believed in the state of phos- 

 phate ;) iron as a peroxide in tobacco, 

 <fcc." In the fruit of the strawberry it 

 has been found ; and the medicinal pro- 

 perties of that fruit are accounted for by 

 many physicians by its presence. De 

 Candolle, in "Physiologie Vegetale," 

 p. 389, asserts that 3650 kilogrammes of 

 copper are consumed annually in France 

 in the article of bread ; and M. Sarzeau 

 says that 560 kilogrammes of the same 

 mineral are swallowed aunually in France 

 in the article coffee alone. 



How these mineral substances are 

 taken up by vegetables is no less curious 

 than their presence in them. Most che- 

 mists believe they are in some way or 

 other taken up by the roots. The experi- 

 ments of John upon this matter, as quoted 

 by Dr Lindley (" Theory of Horticulture," 

 p. 357), would lead us to believe that 



VOL. II. 



they are supplied from the atmosphere as 

 well ; for John "found that the Ramalina 

 fraxinea and Borrera ciliaris, two lichens, 

 contained a large quantity of the last 

 metal, although he could not find a trace 

 of it in the fir-tree, on the topmost 

 branches of which the lichens grew. We 

 cannot, therefore, suppose that such things 

 are the result of accident, and that it is 

 unimportant to the plants containing 

 minerals thus constantly, whether such 

 substances are present in their soil or 

 not." We are afraid that some of our 

 agricultural chemists have jumped at 

 conclusions hurriedly, and drawn deduc- 

 tions which will not bear the test of close 

 investigation. When they give us to 

 understand, that because a crop of wheat, 

 for example, abstracts 76.22 lb. of mine- 

 ral substances from the soil per acre, 

 per annum, consisting of potash, soda, 

 magnesia, phosphoric acid, sulphuric 

 acid, and chlorine, that the same weight 

 (viz. 76.22 lb.) of these ingredients, con- 

 tained in special manures, is the exact and 

 proper return to be made for that abstracted 

 by the crop, so as to leave the soil in the 

 condition in which it was previous to the 

 seed of the crops being sown. 



Such calculations as these appear to 

 have been made without duly considering 

 atmospheric effects, because it appears 

 there has been no allowance made for 

 them. " Plants feed more by their leaves 

 than by their roots." — Lindley. " It is 

 commonly supposed that plants derive 

 the whole of their food from the soil, but 

 this is a great error. It is a fact well 

 ascertained by chemical experiments, 

 that plants derive the greater part of their 

 nourishment from the air, although the 

 soil is equally essential to their growth." — 

 Solly, in Rural Chemistry, p. 96. "Plants 

 possibly draw from the atmosphere more 

 than agriculturists commonly suppose; 

 and the soil furnishes, independently of 

 saline and earthy substances, a proportion 

 of organic matter larger than certain phy- 

 siologists admit." — Boussingault. "The 

 leaves spread out their broad surfaces into 

 the air for the same purpose, precisely, as 

 that for which the roots diffuse their 

 fibres through the soil; the only difference 

 being, that, while the roots suck in chiefly 

 liquid, the leaves inhale almost wholly 

 gaseous food. In the daytime, whether in 

 the sunshine or in the shade, the green 



D 



