12 



CULINIRY OR KITCHEN iSARDEN. 



§ 4. — ROTATION OF CROPS. 



, The necessity of a rotation of crops — 

 that is, not sowing or planting the same 

 ground with the same species of seed or 

 plants from which it has been cleared, 

 but introducing a succeeding crop of as 

 dissimilar a kind as possible — is founded 

 upon two facts, namely, the excrementi- 

 tions of the plants, and the exhausting of 

 the soil by them. Brugmanns supposed 

 he had discovered that some plants exude 

 an acid fluid from their spongioles, which 

 may be regarded as a peculiar kind of 

 excretion, which becomes obnoxious to 

 roots of the same kind, but not so to those 

 of another species; and Macaire asserts that 

 this property is almost general throughout 

 the vegetable kingdom. De Candolle was 

 of this opinion, and conjectured that the 

 soil was not only rendered unfit for the 

 growth of the same species in consequence 

 of these excretions, but believed that, 

 acting as a manure, they improved the 

 soil for other species. This, coupled 

 with the supposition that plants cannot 

 digest their own excretions, seemingly ex- 

 plains to us why the soil becomes dete- 

 riorated by one kind of plant having long 

 grown in it, and its unfitness to support 

 a crop of the same kind until the fecal 

 matter in it shall have become decom- 

 posed. Daubeny and Gyde deny this, 

 and say that these excretions are not in- 

 jurious. 



Gyde's opinion was, that though plants 

 have no power of selection, " but take into 

 their texture any solution offered to theuf 

 roots, they have little or no power of 

 again excreting it; that any excretions 

 are only of the true sap ; and that plants 

 watered with excretions receive no injury 

 by it." This opinion has occupied, to 

 some extent, the attention of physiologists 

 within these two or three years, but, as 

 it appears, as yet without any conclusive 

 result having been arrived at. 



In connection with this, Dr Lindley 

 remarks ("Theory of Horticulture," p. 

 21), "In addition to their feeding proper- 

 ties, roots are the organs by which plants 

 rid themselves of the secreted matter, 

 which is either superfluous or deleterious 

 to them. If you place a plant of succory 

 in water, it will be found that the roots 

 will, by degrees, render the water bitter, 

 as if opium had been mixed with it ; a 



spurge {Euphorbia) will render it acrid, 

 and a leguminous plant mucilaginous; 

 and if you poison one half of the roots 

 of any plant, the other half will throw 

 the poison off again from the system. 

 Hence it follows, that if roots are so cir- 

 cumstanced that they cannot constantly 

 advance into fresh soil, they will, by de- 

 grees, be surrounded by their own excre- 

 mentitious secretions. It would also seem 

 to follow that, under the circumstances 

 just named, they would be poisoned, be- 

 cause they have little power of refusing 

 to take up whatever matter is presented 

 to them in a fitting state. But it is by 

 no means certain that the excrementitious 

 matter of all plants is poisonous either 

 to themselves or to others ; and there- 

 fore the consequences of roots growing in 

 soil from which they cannot advance are 

 uncertain, and only to be judged of by 

 actual inquiry into the nature of the se- 

 cretions." On the power of selection of 

 food, the same high authority observes 

 (p. 18), "Powerful as the absorbing action 

 of roots is found to be, those organs have 

 little or no power of selecting their food; 

 but they appear in most cases to take up 

 whatever is presented to them in a suffi- 

 ciently attenuated form. Their feeding 

 properties depend upon the mere hygro- 

 metrical forCe of their tissue, set in action 

 in a peculiar manner by the vital prin- 

 ciple. This force must be supposed to 

 depend upon the action of the capillary 

 tubes; of which every part of a vegetable 

 membrane must of necessity consist, al- 

 though they are in all cases invisible to 

 the eye, even when aided by the most 

 powerful microscopes. Whatever matter 

 is presented to such a set of tubes will, 

 we must suppose, be attracted through 

 them, provided its molecules are suffi- 

 ciently minute ; and as we have no reason 

 to believe that there is, in general, any 

 difference in the size of the molecules of 

 either gaseous matter, or fluids consisting 

 principally of water, it will follow that 

 one form of such matters will be absorbed 

 by the roots of plants as readily as an- 

 other. For this reason plants are pecu- 

 liarly liable to injury from the presence 

 of deleterious matter in the earth ; and it 

 is probable that, if in many cases they 

 reject it, it is because it does not acquire 

 a sufficient state of tenuity, as iu the case 

 of certain coloured infusions. 



