66 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the latter stages of their history by the action of vegetable and 

 animal life, and their products. When once a soil has been 

 brought under cultivation, the continual ploughing, digging, 

 hoeing, stirring, and other operations of the gardener — all com- 

 prehended under the term " tillage " — assist most powerfully the 

 weathering influences, and cause cultivated soils to become finer 

 and more permeable, and consequently in that respect better and 

 better. 



The purposes of tillage are twofold. First, it improves the 

 texture of the soil in the mere mechanical sense ; or, in other 

 words, it stirs and loosens the soil so that the roots of plants 

 may readily pass through it. Air and water are allowed to enter 

 freely, and water is enabled to pass easily through the mass, 

 while at the same time it ensures that the soil shall retain a 

 sufficient amount of moisture for plant-life. 



Secondly, tillage alters the position and condition of the soil 

 particles, facilitating the chemical changes in these particles 

 through the action of atmospheric agencies. Helping also the 

 microscopic organisms in their work of nitrifying the organic 

 matters contained in the soil. 



The weight of soil on an acre of land is so enormous that 

 small proportions of plant-food present in it may amount to 

 very considerable quantities when reckoned up to the acre at any 

 given depth. Table I. illustrates the weight of different de- 

 scriptions of soil, cut to 9 inches deep, when perfectly dry and 

 free from stones. 



TABLE I. — Weight of an Acre of Soil, cut to 9 inches deep, Dry and 

 Free from Stones. 



Pounds. 



Sandy soil \ 3,500,000 



Arable loamy soil 3,000,000 



Pasture soil 2,250,000 



Forest soil 1,500,000 



Peaty soil 1,000,000 



These illustrations show that an acre of sandy soil will weigh 

 3,500,000 lbs. ; an ordinary arable loamy soil 3,000,000 lbs. ; 

 a pasture soil when dried and the visible roots removed will 

 weigh about 2,250,000 lbs. ; a forest soil that contains an 

 abundance of decaying vegetable matter will weigh but 

 1,500,000 lbs. per acre ; while an acre of peaty soil cut to 

 9 inches deep, in consequence of its light and spongy character, 



