CHAP, v.] Soil and Situation 103 



more binding. The tendency of soils to expand with mois- 

 ture, and to shrink on parting with it again, is practically 

 proportional to its tenacity. Soils may be classified in this 

 respect as 



Heavy, stiff, or tenacious soils, which fissure and crack deeply when 

 dried up. Clays and clayey loams, limes and marls belong to this 

 class. 



Mild soils, exhibiting superficial cracks when suddenly dried up, but 

 which when nearly dry have the power of retaining the form of 

 clods. They are usually composed of favourable admixtures of 

 clay, sand, and lime, as in loams, sandy loams, and loamy limes. 



Light soils, capable of forming clods when moist, but when dry show- 

 ing a strong tendency to disintegrate, as in the case of loamy sands 

 and sandy marls. 



Loose soils, which even when moist have little tendency to form clods. 

 To this class belong the poorer sandy soils. 



Shifting soil, liable in a dry condition to be carried away by the wind, 

 as in the case of sand-drifts and dunes. 



In a light soil, which is not deficient in moisture, humus, and 

 mineral nutrients, a maximum of rootlets can be developed, 

 and through these the maximum of timber. Hence one finds 

 the greatest increase in cubic contents, and in particular the 

 greatest average annual increment in height, on alluvial 

 deposits having finely pulverized particles. But when loose 

 soils are wanting in soil-moisture, planting operations are 

 apt to be unsuccessful ; for the plants have great difficulty 

 in establishing themselves so as to send down their roots 

 to lower levels and thus obtain an assured supply of the 

 water requisite for transpiration through the foliage. Thus, 

 on the sandy soils in some parts of Sussex, for example, 

 seedling Oaks are only found to thrive when planted out 

 among weeds, such as brambles, which keep patches of soil 

 here and there cool and moist. 



The degree of moisture contained in any soil is one of the 

 most important factors concerning woodland growth. No 

 plant can grow without imbibing supplies of water; it is 

 requisite for germination ; without it, the nutrient salts could 



