On the Rotation of Crops. 



289 



substances or gases derived from^ or emitted by, the roots. Per- 

 sons v/ho are inclined to doubt may readily satisfy themselves 

 of the correctness of the statement by sowing a small quantity 

 of peas, beans, or cabbage, in a box or seed-pan, employing 

 the simplest light loam they can procure. After a time, when 

 the plants shall be grown of a size fit to be removed, the earth, 

 upon stirring it, will be found saturated with the peculiar 

 scent which is distinctive of each species. Every vegetable, to a 

 greater or less extent, operates in a like manner, diffusing through 

 the ground certain substances which may justly be viewed as fecal 

 or excrementitious, whether they consist of gaseous or fluid exu- 

 dations, in the strict sense of the term, or merely of exfoliations 

 or fibrous matter separated from the roots. The positive and 

 specific odour is the first proof of this fact ; connected with which 

 is the deepened shade of colour imparted to the earth.'"^ 



2nd. The operation of decomposable manures offers the second 

 proof presumptive of the excretory functions of vegetables. All 

 these manures contain, or are resolvable into, the substance now 

 called humus, of which charcoal (carbon) is the chief constituent 

 and the source of colour. Carbon, oxygen, hydrogen, occasion- 

 ally azote, are the ultimate elements of humus, and of all vege- 

 table dead matter. These elements are susceptible of an infinite 

 variety of modified combinations, when governed by the vital prin- 

 ciple, under the stimulus of the great natural agents. 



Manures, therefore, are the pabulum of vegetable life; they 

 feed and support it : if then there be no antagonist principle in 

 operation, the due and proportionate application of manure would, 

 as far as food is concerned, bring every plant to perfection which 

 is placed in a bed of earth adapted to the structure of its roots. 

 But manure (the most perfect humus) fails to nourish ; it does 

 not, and cannot, support a crop of any individual vegetable which 

 follows in continued or even too frequent succession ;y and there- 

 fore it is clear, to demonstration, that exhaustion is not the cause 

 of failure. 



3rd. But plants which dwindle when so circumstanced, how- 

 ever high may be the condition of the land, succeed perfectly, and 

 produce ample crops, when they follow others in the order of due 

 rotation. Here, then, we perceive that nature furnishes ample 



I cannot say that I have myself ever remarked this peculiar odom-, and 

 I think it would be difficult to find any perceptible difference between the 

 scent of a barley or a wheat stubble ; though it is not improbable that land 

 from which a rank vegetable crop has been removed, may be imbued with 

 the smell of the decomposed roots and leaves which have rotted in the 

 soil. — F. Burke. 



t Is not this contradicted by the fact that beans and wheat, as well as 

 beans, cabbages, and potatoes, though planted successively for years toge- 

 ther, will produce fine crops, if the land be good and well manured? 

 — F. Burke. 



