306 OF DRAINING, AND ITS EFFECTS. 



when the pine forests of Sweden are burned down, a young growth of 

 birch succeeds, but after a time the pines again appear and usurp their 

 former dominion. The soil remains, still, more propitious to the growth 

 of the latter than of the former kind of tree. 



We may, therefore, take a practical lesson from the book of nature. 

 If we wish to have a luxuriant vegetation upon a given spot, we must 

 either select such kinds of seeds to sow upon it as are fitted to the kind 

 of soil, or we must change the nature of the land so as adapt it to our 

 crop. And, even when we have once prepared it to yield abundant re- 

 turns of a particular kind, the changes we have produced can only be 

 more or less of a temporary nature. Our care and attention must still 

 be bestowed upon it, that it may be enabled to resist the slow^iatural 

 causes of alteration, by which it is gradually unfitted to nouriSli those 

 vegetable tribes which it appears now to delight in maintaining 



Let us now turn our attention, therefore, to the methods by which 

 these beneficial changes are to be effected and maintained. 



§ 2. Of draining, and its effects. 



Among the merely mechanical methods by which those changes are 

 to be produced upon the soil, that are to fit it for the better growth of 

 valuable crops, draining is now allowed to hold the first place. That it 

 is an important step in heavy clay lands, and that it must be xha jirst step 

 in all cases where water abounds in the surface soil, will be readily con- 

 ceded ; but that it can be beneficial also in situations where the soils are 

 of a sandy nature — where the subsoil is light and porous — or where the 

 inclination of the field appears sufficient to allow a ready escape to the 

 water, does not appear so evident, and is not unfrequently, therefore, a 

 matter of considerable doubt and difficulty. It may be useful, then, 

 briefly to state the several effects which in different localities are likely 

 to follow an efficient drainage of the land : — 



1°. It carries off" all stagnant water, and gives a ready escape to the 

 excess of what falls in rain. 



2°. It arrests the ascent of water from beneath, whether by capillary 

 afition or by the force of springs — and thus not only preserves the sur- 

 face soil from undue moisture, but also frees the subsoil from the linger- 

 ing presence of those noxious substances, which in undrained land so fre- 

 quently lodge in it and impair the growth of deep-rooted plants. 



3°. It allows the water of the rains, instead of merely running over 

 and often injuriously washing the surface, to make its way easily 

 through the soil. And thus, while filtering through, not only does the 

 rain-water impart to the soil those substances useful to vegetation, which, 

 as we have seen, [see Lecture II., p. 37, Lecture IV., p. 69, and Lecture 

 VIII., p. 159,] it always contains in greater or less abundance ; but it 

 washes out of the upper soil, and, when the drains are deep enough, 

 out of the subsoil also, such Hoxious substances as naturally collect and 

 may have been long accumulating there — rendering it unsound and 

 hurtful to the roots. The latter is one of those benefits which gradually 

 follow the draining of land. When once thoroughly effected, it consti- 

 tutes a most important permanent improvement, and one which can be 

 fully produced by no other available means. It will be permanent, 

 however, only so long as the drains are kept in good condition. The 



