Green Vegetable Manure. l X\ 



Without referring to the analogy, which could be easily 

 proved to be incorrect, and a weak and inefficient prop to 

 the argument, I think I shall have little difficulty in convinc- 

 ing you and the public, that the comparative experiment, al- 

 though it was apparently conclusive, yet, was incomplete 'and 

 unsatisfactory ; inasmuch as no use appears to have been made 

 of the thermometer, for ascertaining the comparative degree 

 of heat of the soil, in the portions of the field when manured 

 in the manner already described, both when the turnip seed 

 was sown, and at different periods of the growth of the plants. 

 To this neglect, I conceive may be attributed the fallacy of 

 the conclusions, which have been deduced from so well 

 planned an experiment. 



I am aware that, in opposing the opinions of so truly phi- 

 losophical an enquirer into vegetable physiology as Mr. Knight 

 is, I expose myself to the hazard of being stigmatized with 

 presumption ; but, I am also convinced, that as truth alone 

 is the object of that gentleman's researches, he will receive 

 with candour any objections to his opinions which are fairly 

 advanced. I have, therefore, no hesitation in asserting, that 

 before we can admit the correctness of the opinion, which 

 assumes that the superiority of the crop, on the portion of 

 the field manured with the green fern, was owing to the more 

 easy re-organization of the recent vegetable matter employed 

 as manure, by the living powers of the growing plants, the 

 author of it is bound to demonstrate how any vegetable sub- 

 stance contained in the soil, in a state not reduced to its 

 ultimate components, can be taken up by the absorbents of 

 the radicles of plants ; and, also, how any vegetable substance, 

 without being so reduced, can be rendered sufficiently soluble 

 in the soil to enter the mouths of these minute vessels ? I 

 am willing to admit that the secretions of some plants are 

 altered by situation, and the nature of the soil in which they 

 grow: as for example, in the change from potash to soda, 

 which occurs in plants brought from inland situations and 

 cultivated near the sea. But, it must be remarked, that these 

 changes are found to occur in the saline secretions only, which 

 are remarkably soluble. Linnaeus, indeed, maintained, that 

 the .secretions of plants very different from one another in 

 genera and species, growing on the same soil, exist ready 

 prepared in the earth, and are merely selected by the plants : 

 but this opinion has been long since regarded as untenable. 

 The living powers of both animals and plants seem to be per- 

 fectly adapted for recombining substances the most opposite 

 and incongruous, and assimilating them to their own proper 

 nature. What can be stronger proofs of this fact, than that 



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