30 LOCALITY AND FOREST VEGETATION. 



r. Ca)yiiiiii In hohl Wafer. 

 It is generally proportional to the percentage of tine earth 

 and humus in the soil. 



>/. HlfijrOftropicill/, 



or the capacity of the soil to attract and condense aqueous 

 vapour from the atmosphere. It depends on the degree of 

 division of the particles, and on the temperature. The liner 

 the division, the greater the hygroscopicity ; more vapour is 

 condensed at a low than at a high temperature. Soils rich in 

 humus show the greatest hygroscopicity, next clay, then loam, 

 then lime soils, and it is smallest in sand. 



e. TenarHi/ in reUtinhuj Moisture 

 is greatest in clay soils, moderate in calcareous soils and 



smallest in sand. 



/. I'lrmeahilitji, 



or the capacity to let water pass through, is greatest in sand, 

 especially if of a coarse grain, and smallest in clay. Humus 

 soil approaches clay, while calcareous soils and loam stand 

 about half-way betw^een the two extremes. Stiff clays are 

 liable to be altogether impermeable ; in many cases the clay of 

 a mixed soil is gradually carried into the subsoil, where it 

 forms an impermeal)le layer, frequently bound together by 

 oxide of iron. 



(J. The Power to retain Satta dissolved in Water 

 depends on the proportion of line earth in the soil. 



//. 'Hie ( 'aparitij to liccome Heated 

 is greatest in sand, and smallest in clay. Calcareous soils 

 approach sand ; loam approaches clay. Sand and calcareous 

 soils are generally hot soils, while clay is a cold soil. 



/. (li)ierat. 

 Depth intensities the etliect of the various physical proper- 

 ties. A depth of 4 feet may be considered as sufficient for 

 almost any species, and many can do with considerably less. 



