140 CHOICE OF SOILS. 



which plants may fix their roots and sustain an erect position, also to 

 supply inorganic food to plants at all periods of their growth, and to 

 act as a medium for the chemical changes essential to the preparation 

 of their food. In noticing the constituents of soils, we have omitted 

 to mention traces of several others, yet these, in a rigid chemical 

 analysis, are of some importance. Still, as most of our readers are 

 supposed to have but a limited acquaintance with the nature of these 

 constituents, or with the means by which they can be rendered practi- 

 cally useful, it would be of no possible use to go into minute details. 

 But, from what has been said, it will be perceived that some lands are 

 well adapted and others ill-adapted to particular kinds of crops, and 

 that it is of the first importance to perceive and tq practice upon these 

 facts. 



In our remarks on vegetable geography it will have been seen 

 that particular wild plants, in accordance with their natural habits or 

 preferences, have uniformly selected particular places for their habi- 

 tations, nor should we be blind to the fact that this is as much in ac- 

 cordance with their choice as it is for animals habitually to select and 

 retain certain places as most agreeable to them and as best affording 

 them the means of life, health and the propagation of their species. 

 Salt-loving plants, as a consequence, select the borders of the sea shore 

 or salt lakes ; and thus with most species and genera of plants, as 

 seen in our view of their particular localities. Art may, however, 

 adapt the soil to suit the requirements of particular plants and induce 

 their location and growth, while other plants will not, or cannot be 

 made to thrive on certain soils, any more than animals which are not 

 there accommodated with the means of growth and enjoyment. One 

 kind of grass only will grow on peaty soils ; but, if this be limed, 

 green crops will spring up ; yet, requiring other elements, they will 

 produce much straw but no fruit. For them to nourish, therefore, 

 the soil must be furnished with other materials. Mare's-tail abounds 

 on the margin of streams ; and, if these streams contain much car- 

 bonate of lime, water cresses will spring up and flourish along its sides 

 and shallow bed. The red clover and the vetch are delighted in the 

 presence of gypsum, and white clover in alkaline matter, and some 

 heaths will show themselves above serpentine rocks. The alternations 

 of forest trees and of various other plants, lor these reasons, we have 

 elsewhere spoken of; and we might enumerate other remarkable 

 instances. These show the chemical constitution of the soil, and that 

 when it is deprived of the constituents essential to the growth of one 

 kind of plants, they will disappear and others will take their place, for 

 the growth of which the soil may be much better fitted. We only 

 follow nature herself, therefore, in rotating crops. 



The soil often becomes sick or tired of a certain crop or plant, and 

 thus indicates a change in its chemical composition; but it may 



