THE PRINCIPLES OF ENGLISH AGRICULTURE. 27 



a manner that they cannot be again washed out. Such 

 power is a property of porous substances generally, and is 

 shared by soils. All fertile soils possess it, and by it they 

 are able to retain fertilizing matter for the use of plants. 



Further, it is extraordinary that this power is exerted with 

 the most marked effect upon those substances which crops 

 require in the greatest abundance namely, ammonia, potash, 

 and phosphoric acid. A soil compounded in the manner 

 described is able to seize upon soluble matter as it is produced 

 by disintegration slowly acting upon the mineral wealth of 

 the soil, and to retain such material and hold it diffused 

 throughout the bulk of the soils. Thus the soil becomes 

 charged or permeated with matter which can be taken up by 

 the roots of plants. 



Let us now turn our attention to the extraordinary action of 

 vegetation as a factor in the formation of soils. I remember 

 being struck by a passage in Mr. Oliver Wendell Holmes's 

 Autocrat of the Breakfast Tablet i n which he noted the way 

 in which nature is ever ready to place a germ or seed 

 wherever there is a crevice however minute to receive it. 

 She takes possession of rocky surfaces long before they are 

 fit for cultivation or to bear what we call crops, even of grass. 

 Long before decay has actually broken down the rocky texture 

 vegetation places her earliest outposts, and thus helps to 

 expedite that degradation of material which ultimately give 

 us soil. The lichen which tempers and softens the colour of 

 a newly-built wall, the brown or varied colour which we rely 

 upon to tone down the gaudy appearance of a newly-built 

 house, is nothing but the advance guard of vegetation. So 

 also is the moss which requires to be cleaned off the roofs or 

 to be removed from inscriptions ; or the ivy which creeps 

 over walls, while beautifying them hastens their decay. 

 Vegetation has many methods of attack, but the result is 

 always a more rapid decay. The mycelium of a 1 fungus or 



