160 



FARMERS' REGISTER— EXCRETIONS OF PLANTS. 



raised from the de[)th of two or three feet below 

 the surface, it will generally be found of a differ- 

 ent color Irom the old worked soil of the garden or 

 field. A hazel-loam, which is a combination of 

 sand; aluminous and chalky impalpable matter, 

 colored by oxide of iron, is frequently found at the 

 depth mentioned, and may be considered pure vir- 

 gin earth. If such soil be planted with strawber- 

 ries, or almost any vegetable crop, its color will un- 

 dergo a change, and become many shades darker. 

 Is this change of tint effected by carbonaceous mat- 

 ter excreted from the roots, by the decomposition 

 of carbonic acid derived from the air, or by the 

 partial de-exiodation of the ferruginous constituent 

 of the earth? The latter maj^ probably operate to 

 a certain extent, but I hold it more philosophical 

 to conclude that the change in color is to be as- 

 cribed to hydrogen gas (holduig, perhaps, carbon 

 and other matters in solution,) emitted from the 

 roots into the soil, and therein effecting chemical 

 decompositions by specific elective, or rather elec- 

 tric attractions. 



This blackening of the soil may be suspected 

 by some to proceed from the decomposition of car- 

 bonaceous matters; and it is highly probable that 

 it does so proceed; but even admitting that ma- 

 nures have been placed in the soil, their decoinpo- 

 sition and absorption, according to the received 

 opinion, by the roots of the crop, ought to abstract 

 the carbon from the soil, and not to deposite it 

 therein ! But I am supposing a case wherein 

 pure \'irgin sandy loam, without manure, is em- 

 ployed; and, to simplify the experiment, I saj' — 

 let a middle-sized garden-pot be filled Avith such 

 soil, and in it let a single vigorous strawberry plant 

 be |)laced in the month of February, and be reg- 

 ularly watered; by the end of August following, 

 that is, about the period when the growing season 

 is almost passed, the soil will be found of a 

 deeper color, by many shades, than it exhibited 

 when placed in the pot. 



My experience has taught me this fact, and I 

 ascribe the effect to the matter emitted by the 

 roots into the earth. Earth so colored, is not, I 

 conceive exhaused: it is doubtless changed, and in 

 time would be incapable of sujijiorting the vege- 

 tation of the plant which had deposited the color- 

 ing matter within it, but in respect to mere abstract 

 quality, it is unquestionably richer than it prima- 

 rily was, having received more than it gave out, 

 and is, in fact, manure for another species of 

 vegetable. 



This is in accordance with the very valuable ex- 

 periment of M. Macaire, which indicates that 

 yellow coloring matter was aflorded by the bean 

 to pure water, which yellow matter was taken up 

 by "|)lants of wheat," that "lived well," and 

 afforded evidence of having "absorbed a portion 

 of the matter discharged by the first" (the 

 beans.) 



My own reflection, and observation of fiicts, have 

 satisfied me that certain plants do emit hydro-car- 

 bonus compounds into the soil, that poison it, inas- 

 much as refers to themselves individually; but such 

 experiments, as those of M. Macaire, are invalu- 

 able, and ought to be persisted in, m conjunction 

 with daily observations of the soil of the field and 

 garden, t'ill the fact in all ils bearing be establish- 

 ed. 1 for one intend, if life be spared to the next 

 spring, to follow the advice given at page 327 of 

 this volume, and to "prosecute those interesting 



investigations" as far as the means within my 

 command ^vill permit, for they can scarcely fail to 

 lead to important results. 



It remains to be observed, that the doctrine of 

 the excretory powers of plants does not strictly 

 apply to all vegetables; at least, it is manitest that 

 trees and many shrubs will live on, and improve 

 in, the same piece of ground lor an almost indefi- 

 nite period. 



Many garden vegetables furnish also exceptions 

 to the rule, and I particularly notice the potato. 

 Fn fact, the experiment of M. INIacaire seems to 

 afford evidence that this vegetable does not secrete 

 matter of any decisive character. I know those 

 who have assured me, that potatoes liave been set 

 for ten or even t^venty years on the same land, 

 with little or no other manure than coal-ashes and 

 the scrapings of road-sand. This sand was, in 

 the county I allude to, obtained from the calca- 

 reous stone of the neighborhood, and it proved a 

 powerful melioratmg substance to the cold clayey 

 soil of the district. 



I venture to suggest, that grain and other crops^ 

 which expend all their vegetative energy upon 

 the production of seed-vessels, are less likely to 

 protrude matter from their roots than other crops 

 which abound with large bulky foliage; they, 

 therefore, cannot prove manure crops for their con- 

 genors, although they may render the soil un- 

 healthy to themselves indiA-idually. With respect 

 to the potato, I think it evident, that its foliage 

 elaborates much vegetative matter, a large portion 

 of which is expended in the production and sup- 

 port of tubers under ground. These tubers are not ' 

 the roots proper, but enlarged processes, the de- 

 positories of jnuch nutritive matter. It is highly 

 probable, that the plants which produce bulbs, tu- 

 bers, or spindle roots, Avhose foliage is abundant 

 or very large, will in general be innoxious to them- 

 selves, at least comparatively so, in consequence 

 of the absorbent powers of their bulky root pro- 

 cesses. They will in proportion also, be of little 

 service to corn or other crops, unless much ma- 

 nure be previously applied. In a word, the vast 

 foliage which they develope, must claim a great 

 supply of raw sap from the soil. This, or the pre- 

 pared portion of it, is returned with interest to the 

 roots, but it is then diverted into peculiar channels, 

 and is employed in the production of those pro- 

 cesses that constitute so large a portion of the food 

 of man and of catffe. The bulb or tuber-bearing 

 plants are generally but indiffisrent preparers of 

 the soil for other crops, for they must exhaust itg 

 decomposable materials; but they may be grown 

 (though not to full perfection perhaps) on the 

 same ground without becoming diseased. Such, 

 I think, will be found to be generally the fact; and 

 this, as far as the experiment goes, has been con- 

 firmed by the observation of M. Macaire. 



From all that has been said, it is, I think, fair 

 to conclude that, although plants decompose and 

 take up the nutritive maUevs of the soil, and render 

 manuring indisj)ensable, yet it is not by exhaustion 

 that a soil is rendered unfit for a repetition of an 

 individual crop. Facts in abundance might be 

 multiplied, in order to prove that a rotation is called 

 for, in consequence of the feculent matter previous- 

 ly deposited affecting the nutritive power of the 

 soil in supporting any individual crop. 



