570 Cultivation of Plants. 



of purity it is white, and receives the name of chalk. In this 

 state it constitutes a poor soil, absorbs little heat from the 

 sun's rays, dissolves under the action of rain, blisters and flakes 

 from frost, laying bare the roots of plants growing upon it. 

 Earth containing from 40 to 60 per cent., the remainder being- 

 composed of equal parts of argillaceous and silicious matter, is 

 termed calcareous, and is generally very favourable for cultiva- 

 tion. It thus constitutes a light soil, easily worked ; but a 

 larger proportion of lime renders it very adhesive when moist. 



Silicious, or sandy soil is diametrically opposite in its 

 physical qualities to argillaceous soils. It is rough or gritty 

 to the touch, light, friable and loose, permitting the passage 

 of water with great facility, drying with the slightest sunshine, 

 and rapidly accumulating heat. Pure silicious sand, such as 

 results from the disintegration of sand^rocks, is in its nature 

 quite unproductive ; but if mixed with a certain proportion of 

 humus, and especially if it contain from 15 to 20 per cent, of 

 argillaceous and calcareous matter, it is suitable for the support 

 of many plants. A warm, poor, well-drained soil of this descrip- 

 tion is eminently favourable for the growth of tender subjects. 

 Fine silicious sandy soil, with sufficient humus or vegetable 

 mould to appear brown or nearly black, plays an important 

 part in horticulture under the name of peat-earth. On account 

 of its lightness it is admirably adapted for raising small seeds, 

 but frequent waterings are necessary in consequence of the 

 facility with which it dries up. It is, moreover, the only soil 

 suitable for the culture of plants that grow naturally in peaty 

 or boggy places, such as Heaths, Ehododendrons, Azaleas, and 

 the Ericaceae generally, and a few members of other families, 

 collectively known as American plants, though in point of fact 

 many of them are not of American origin. 



Combinations of the three principal elements above de- 

 scribed vary exceedingly in their relative proportions, and also 

 by the addition of other matters which modify their physical 

 properties. Hence the term mixed soils, as applied to the 

 soils designated, according to their composition, argillo -arena- 

 ceous, in which lime is almost wholly wanting ; argillo-cal- 

 careous, consisting mainly of clay and lime ; calcareo-silicious, 

 nearly destitute of clay. Ferruginous soil receives its name 

 from the presence of a large quantity of carbonate of iron, 

 giving it a reddish tinge. But these secondary distinctions 

 are of little importance in practical gardening, as the soil, on 



