82 Studies in Forestry [CHAP. iv. 



The demands of the different species of woodland trees 

 vary greatly with regard to mineral nutriment, as can be proved 

 easily by an analysis of the amount of mineral matter found 

 in the ash yielded on combustion and elimination of the 

 non-mineral portions of their tissue (formed by Carbon, Hy- 

 drogen, Oxygen, and Nitrogen). The younger parts of the 

 organism, and especially those actively engaged in the work 

 of circulation, assimilation, and secretion (the foliage and the 

 cambium), yield more ash because they are richer in salts 

 of potash, phosphates, and nitrogenous compounds, than 

 the older portions (the alburnum), and the lifeless tissue 

 in the interior of the stem forming the hard heartwood (the 

 duramen). 



The leaves are much richer in mineral matter than any 

 other part of the plant ; whilst the bark contains more than 

 the wood, and the younger portions of the tree contain more 

 than the older portions. When parts of the tree are about 

 to die off (as, for example, in the case of the foliage of 

 deciduous trees in autumn), the more important classes of 

 mineral nutrients Potash, Phosphoric Acid, Magnesia, Lime 

 are transferred into the still active portions of the organism, 

 to which they wander back together with albuminoid substances 

 and soluble carbo-hydrates. 



The total proportion of mineral matter in the timber of 

 broad-leaved genera of trees is seldom under J% or exceeding 

 i-% of the dry substance of the wood. It usually ranges 

 between 0-3 and 0-45%; but, in the case of Birch and of 

 conifers, it varies from about ^ to -J% (o 17 to 027). The 

 heartwood of old stems contains less ash than the sapwood. 

 It is also comparatively devoid of albuminoid substances, and 

 is therefore more durable, i.e. it is less exposed to the disinte- 

 grating and decomposing influences of alternating damp and 

 heat, or to the organic attacks of saprophytic fungoid growth 

 and insects. 



According to the demands of the different kinds of trees for food- 



