232 SCIENCE OF GARDENING. Part II. 



face irrigation. Where the under-stratum is gravelly, and rests on a retentive stratum, 

 this mode of watering may take place without drains, as it may also on perfectly flat 

 lands, by filling to the brim, and keeping full for several days, surrounding trenches ; 

 but the beds or fields between the trenches must not be of great extent. This practice is 

 used in Lombardy on the alluvial lands near the embouchures of the Po. In Lincoln- 

 shire the same mode is "practised by shutting up the flood-gates of the mouths of the 

 great drains in the dry seasons, and thus damming up the water through all the ramifica- 

 tions of the drainage from the sea to their source. This was first suggested by G. Ren- 

 nie and Sir Joseph Banks, after the drainage round Boston, completed about 1810. A 

 similar plan, on a smaller scale, had been practised in Scotland, where deep mosses had 

 been drained and cultivated on the surface, but where, in summer, vegetation failed 

 from deficiency of moisture. It was first adopted by J. Smith, (See Essay on the Im- 

 provement of Peat-Moss, 1795,) on a farm in Ayrshire, and has subsequently been brought 

 into notice by J. Johnston, the first delineator and professor of Elkinston's system of 

 draining. 



1 101. Manuring by irrigation. Irrigation with a view to conveying additions to the soil 

 has long been practised, and is an evident imitation of the overflowing of alluvial lands, 

 whether in meadow or aration. In the former case it is called irrigation or flooding, and 

 in the latter, warping. Warping is used chiefly as a mode of enriching the soil by an 

 increase of the alluvial depositions, or warp of rivers, during winter, where the sur- 

 face is not under crop, and is common on the banks of the Ouse. 



1 102. The rationale of irrigation is thus given by Sir H. Davy. " In general in nature 

 the operation of water is to bring earthy substances into an extreme state of division. 

 But in the artificial watering of meadows, the beneficial effects depend upon many dif- 

 ferent causes, some chemical, some mechanical. Water is absolutely essential to vegeta- 

 tion ; and when land has been covered by water in the winter, or in the beginning of 

 spring, the moisture that has penetrated deep into the soil, and even the sub-soil, becomes 

 a source of nourishment to the roots of the plants in the summer, and prevents those bad 

 effects that often happen in lands in their natural state, from a long continuance of dry 

 weather. When the water used in irrigation has flowed over a calcareous country, it is 

 generally found impregnated with carbonate of lime ; and in this state it tends, in many 

 instances, to ameliorate the soil. Common river water also generally contains a certain 

 portion of organisable matter, which is much greater after rains than at other times ; and 

 which exists in the largest quantity when the stream rises in a cultivated country. Even 

 in cases when the water used for flooding is pure, and free from animal or vegetable sub- 

 stances, it acts by causing a more equable diffusion of nutritive matter existing in the 

 land ; and in very cold seasons it preserves the tender roots and leaves of the grass from 

 being affected by frost. Water is of greater specific gravity at 42 Fahrenheit, than at 

 32, the freezing point ; and hence, in a meadow irrigated in winter, the water immediately 

 in contact with the grass is rarely below 40, a degree of temperature not at all prejudi- 

 cial to the living organs of plants. In 1804, in the month of March, the temperature in 

 a water meadow near Hungerford was examined by a very delicate thermometer. The 

 temperature of the air at seven in the morning was 29. The water was frozen above the 

 grass. The temperature of the soil below the water in which the roots of the grass were 

 fixed, was 43." Water may also operate usefully in warm seasons by moderating tem- 

 perature, and thus retarding the over-rapid progress of vegetation. The consequence of 

 this retardation will be greater magnitude and improved texture of the grosser parts of 

 plants, a more perfect and ample developement of their finer parts, and, above all, an 

 increase in the size of their fruits and seeds. We apprehend this to be one of the princi- 

 pal uses of flooding rice-grounds in the East ; for it is ascertained that the rice-plant will 

 perfect its seeds in Europe, and even in this country, without any water beyond what is 

 furnished by the weather, and the natural moisture of a well constituted soil. " In 

 general, those waters which breed the best fish are the best fitted for watering meadows ; 

 but most of the benefits of irrigation may be derived from any kind of water. It is, how- 

 ever, a general principle, that waters containing ferruginous impregnation, though pos- 

 sessed of fertilising effects when applied to a calcareous soil, are injurious on soils that 

 do not effervesce with acids ; and that calcareous waters, which are known by the earthy 

 deposit they afford when boiled, are of most use on siliceous soils, or other soils containing 

 no remarkable quantity of carbonate of lime." 



Subsect. 6. Changing the Condition of Lands, in respect to Atmospherical Influence. 



1103. The influence of the weather on soils may be affected by changing the position of 

 their surface and by sheltering or shading. 



1104. Changing the condition of lands, as to solar influence, is but a limited means of 

 improvement ; but is capable of being turned to some account in gardening. It is 

 effected by altering the position of their surface, so as that surface may be more or less 

 at right angles to the plane of the sun's rays, according as heat or cold is to be increased 



