Green Vegetable Manure. 23 



the rapidity of the fermentation will be so moderated, as to 

 prevent the pabulum of the process, if I may so express 

 myself, from being too soon exhausted. Owing to this state of 

 the green Fern, therefore, the germination of the turnip seed 

 sown over it was begun, and the vegetative process carried on 

 in the plants, in a manner somewhat similar to the effect which 

 would follow were the seed sown in a hot-bed; except that the 

 heat was of a more moderate degree, and, consequently, better 

 suited to maintain the functions of the vegetable economy in 

 the growing plant in a healthy state. The fold and stable 

 manure, on account of the ready formed salts it contained, 

 would, perhaps, promote the germination of the seed and the 

 growth of the plants more vigorously for a short time ; but as 

 the process of fermentation would be sooner completed in it 

 than in the green Fern, the supply of heat to the soil would be 

 sooner exhausted, and consequently, that necessary stimulus 

 being withdrawn from the growing turnips on the portion of 

 the field manured with it, the plants over the green Fern 

 would now gain the ascendancy, as they were still supplied 

 with heat; the process of decomposition being yet in activity 

 in the Fern. Again, as the fermentation was altogether over 

 in the completely decayed dung, no heat, or scarcely any, 

 would be extricated from it, and, therefore, the sole benefit 

 which could arise to the germinating seeds and growing 

 plants from this manure, must have proceeded merely from 

 the stimulus of its saline components, and from the carbo- 

 naceous matter in a soluble state, which it is adapted to 

 afford. It may be argued, that, as it is probable, the 

 soluble carbonaceous matter afforded by completely decayed 

 dung is the chief part of the food of plants, the turnips raised 

 over this manure should contain more solid contents than 

 those over the other manures, although their growth was less 

 vigorous and luxuriant. That, however, more food is supplied 

 by completely decayed manure, and yet less taken into the 

 system of the plant, may be equally true ; for the heat afforded 

 by the more recent manures being absent, the action of the 

 vegetable vessels in the growing turnips would be more 

 languid, and absorption and assimilation consequently less 

 perfect; the presence of the stimulus of heat being as essen- 

 tial as the simple supply of nutriment, for the perfection of 

 the plant. That it is heat only which can be regarded as the 

 agent producing the superiority of the crop of turnips, on 

 the portion of the field manured with green Fern, as detailed 

 in Mr. Knight's experiment, may easily be proved by the 

 thermometer, in a repetition of the experiments. Why, 

 therefore, Mr. Knight may say, has the objector to my ex- 



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