WITH REFERENCE TO HORTICULTURE. 7 



when the sun does not shine. A white soil, such as we sometimes find 

 on chalky or marly subsoils, is the longest of all soils in being warmed, 

 because by all white surfaces the rays of light and heat are reflected, 

 while by all black surfaces they are absorbed. Hence, taking into 

 consideration colour, texture, and aspect, a dark sandy soil, on a sur- 

 face exposed to the south or south-east, must be the warmest of all 

 soils; and a moist white clay of compact texture, similarly exposed, 

 the coolest. The aspect is not only of importance with reference 

 to the influence of the sun in warming or cooling the soil, but also 

 as to its effects in maturing the produce which grows on it. 



The plants which grow on a soil are the surest indications, to a prac- 

 tical botanist and cultivator, of the actual state of that soil with refe- 

 rence to culture j though they do not always indicate the improvement 

 of which the soil is susceptible. Marshy soils are indicated with con- 

 siderable certainty both by herbaceous and ligneous plants, as are also 

 very dry soils ; but the earths of fertile soils cannot be so readily 

 inferred from the plants growing on them. Thus thorn hedges will 

 be found growing vigorously alike on clays, sands, and chalks ; though 

 never on these soils, or on any other, when they are either very dry, 

 or saturated with water. Some few plants, when found in their native 

 stations in considerable quantities, may be considered absolute in 

 respect to the earths of the soil in which they grow ; such as the 

 Tussilago Farfara, which always indicates clayey soil ; Clematis Vitalba, 

 calcareous soil ; Arenaria rubra, sandy soil ; Rumex Acetosa, ferru- 

 ginous soil; Vaccinium uliginosum, peaty soil; Salicornia herbacea, 

 saline soil ; Caltha palustris, marshy soil, &c. : but by far the greater 

 number of plants only indicate the state of a soil relatively to water 

 and organic matter. In short, nature may be said to have only three 

 kinds of soil relatively to plants ; the dry, the moist, and the fertile. 



The Improvement of Soils, with a View to Horticulture. 



Having seen, in the preceding section, that the permanent fertility 

 of a soil depends mainly on its condition relatively to water and heat, 

 it follows that the improvement of soils must be principally directed 

 to increase their capacity for absorbing and retaining these elements 

 in the degree most suitable for vegetation. The principal operations 

 for this purpose are : draining, to withdraw superfluous water from 

 soils ; and mixture and pulverization for improving their texture, in 

 order to admit more readily the moisture and heat of the atmosphere. 



Draining is the principal means for altering the condition of a soil 

 with reference to water. Soils are affected by rains from above and 

 springs from below ; the former are carried off" by open gutters, and 

 the latter by covered channels. All draining is founded on the well- 

 known hydrostatic law by which all fluids have a constant tendency to 

 arrange themselves in a horizontal position. Hence, to carry off water, 

 either from a surface or a subsoil, it is only necessary to form channels 

 above or under ground in an inclined position. The kind of drains, 

 and the number employed in any given case, will depend on the 



