278 HANDT-BOOK OF HUSBANDRY. 



" According to the preceding views, plants must obtain from 

 " the soil certain constituents, in order to enable them to reach 

 " perfect maturity— that is, to enable them to bear blossoms and 

 " fruit. The growth of a plant is very limited in pure water, in 

 " pure silica, or in a soil from which these ingredients are absent. 

 " If there be not present in the soil alkalies, lime, and magnesia, 

 " the stem, leaves, and blossoms of the plants can only be formed 

 " in proportion to the quantity of these substances existing as a 

 " provision in the seed. When phosphates are wanting, the seeds 

 " cannot be formed. 



" The more quickly a plant grows, the more rapidly do its leaves 

 " increase in number and in size, and therefore the supply of 

 *' alkaline bases must be greater in a given time. 



" As all plants remove from the soil certain constituents, it is 

 " quite obvious that none of them can render it either richer or 

 *' more fertile for a plant of another kind. If we convert into 

 '' arable land a soil which has grown for centuries wood, or a 

 *' vegetation which has not changed, and if we spread over this 

 *' soil the ashes of the wood and of the bushes, we have added to 

 " that contained in the soil a new provision of alkaline bases, 

 *' and of phosphates, which may suffice for a hundred or more 

 *' crops of certain plants. If the soil contains silicates susceptible 

 " of disintegration, there will also be present in it soluble silicate 

 '' of potash or soda, which is necessary for the rendering mature 

 " the stem of the siliceous plant ; and, with the phosphates 

 *' already present, we have in such a soil all the conditions neces- 

 ** sary to sustain uninterrupted crops of corn for a series of years. 



" If this soil be either deficient or wanting in the silicates, but yet 

 " contain an abundant quantity of salts of lime and of phosphates, 

 *' we will be enabled to obtain from it, for a number of years, suc- 

 " cessive crops of tobacco, peas, beans, etc., and wine. 



" But, if none of the ingredients furnished to these plants be 

 " again returned to the soil, a time must come when it can no 

 " longer furnish these constituents to a new vegetation, when it 

 " must become completely exhausted, and be at last quite sterile, 

 " even for weeds. 



