5St FollKST LITTKi:. 



tlie iiu-ans of (lisintc'<,niitin<,' the subsoil and renJcrin- 

 the nutritive matter contained in it soluble. 



i. PhVSICAI. ACIION iiK HlMlS. 



'riic physical action of humus is beneficial owing; to its power 

 of absorbing:; water and watery vapour, as well as some of the 

 most nutritious mineral substances (potash, phosphoric acid, 

 ammonia, &c.), from their soluble compounds and supplying 

 them to plants ; also for its retention of heat. 



Fine earthy particles have similar properties, but not more so 

 than humus. The soil-strata containing the roots of plants is 

 thus protected, to a certain extent, from loss by drainaire of 

 these important substances. 



ii. Rksiih-al PiioiH'cTs ok Dkcomi'osed Hi'Mrs. 



The residual products of decomposed humus are ash, carbon 

 dioxide and water ; they form, partly alone and partly in com- 

 bination as salts, the nutritive material or manure for the 

 forest. In the ash resulting from the decomposition of humus, 

 the nutritive mineral substances which have been taken from 

 the soil for the production of wood are returned to it in a 

 form that is most easily assimilable. 



The extent to which nutritive mineral matter, the so-called 

 ash-constituents of a soil, furthers the growth of plants, is 

 proved by the effects of manure in agriculture, the improved 

 growth of manured forest nurseries and the enhanced wood- 

 ])roduction of minerally rich, as compared with minerally poor 

 soils. Trees retain the ash-constituents in different degrees in 

 their several parts, and at different seasons of the year. Tlie 

 stem is poorest in this respect, the more so the older it is ; 

 green branches are richer in ash the younger they are ; still 

 richer is the bark, especially in the upper parts of the tree. 

 Leaves and needles, however, contain the greatest proportion 

 of ash. 



