1204. A certain degree of friability or looseness of texture is required in soils, in order that the operations of culture may be easily conducted; that air and moisture may have free access to the fibres of the roots, that heat may be readily conveyed to them, and that evaporation may proceed without obstruction. These are commonly attained by the presence of sand. As alumina possesses all the properties of adhesiveness in an eminent degree, and silex those of friability, it is obvious that a mixture of these two earths, in suitable proportions, would furnish every thing wanted to form the most perfect soil, as to water and the operations of culture. In a soil so compounded, water will be presented to the roots by capillary attraction. It will be suspended in it, in the same manner as it is suspended in a sponge, not in a state of aggregation, but of minute division, so that every part may be said to be moist, but not wet. (Grisenthwaite.) Air will also penetrate through the particles of such a soil in the same manner as water.