31 



months of the summer, when food of all kinds is required 

 and assimilated by the plant, but perishes in the colder 

 months, when vegetation is nearly dormant and scarcely any 

 nourishment required, must preclude the opinion that the 

 want of food of any description whatever is concerned in its 

 destruction. 



Will an excretion, or rather the emission of excremen- 

 titious matter from the roots of clover, account for its dis- 

 appearance ? for in this opinion Professor Liebig coincides 

 with that of the Committee of the Yorkshire Agricultural 

 Society. But against such an agent being concerned, it may 

 be urged in the first place, that there are certain light lands 

 which have been reclaimed some 30 years ago, and therefore 

 never have produced clover at any former period, but upon 

 which the crop always disappears in the winter. A farm 

 near Barnsdale bar, on the Magnesian Limestone ; several 

 farms on the south side of Darrington, on the same geolo- 

 gical formation ; and certain portions of the Yorkshire 

 Wolds are in this predicament. No excrementitious matter, 

 therefore, can destroy the clovers on these farms, because 

 they have never grown the plant. Macaire Princep found 

 that the Leguminosse (to which family the clovers belong) 

 emitted gum and carbonate of lime. But the gums are very 

 soluble in water, and therefore would be easily washed out of 

 the soil ; and it seems very extraordinary that in the heavier 

 soils, consisting of loam and clay of the New Red Sandstone, 

 this gum trifolii should only remain three years, while in the 

 lighter soils of the Magnesian Limestone eight years, but in 

 the still more open and porous soils of the Chalk Wolds it 

 endures twelve years. In fact this wonderful substance, con- 

 trary to the known law of eremacausis, decomposes more 

 slowly in proportion to the porosity of the soil, and in those 

 containing the most calcareous matter. Again, if this excre- 

 tion can remain in the soil nearly twelve years, it must be 



