DURABILITY. 25 



fungi ; moreover, the heavier wood may be more subject to cracks 

 through which fungus spores may at once get admittance into 

 their interior. Nevertheless the heavier woods are generally also 

 the more durable. In the case of specimens of one and the same 

 species, this rule is universally true, since the closer the tissues are, 

 the less room is there for the entry of spores. -Hence the timber 

 of trees grown in favourable soils and localities, and in the full 

 enjoyment of light and warmth, is more durable than that of trees 

 grown under less favourable conditions. This proves the necessity 

 of thinning timber forests properly, and the superiority of methods 

 of culture which give the future timber trees room for unrestricted 

 development. 



The sapwood, being full of moisture and of starch an'd other 

 reserve materials, decays very quickly, although there are some 

 extremely durable woods, such as teak, thin rafters of which, if 

 properly seasoned, last for over 20 years. In old large trees the 

 wood near the centre has generally already undergone a certain 

 amount of decomposition, and hence is subject to early decay. 

 There are two exceptions to this rule — (1), species in which ebony 

 is formed, and (2), conifers rich in resin, the central zones of 

 which are generally impregnated with this substance. 



The season in which a tree is felled has a powerful influence on 

 the durability of its timber. The most durable wood is obtained 

 if the tree is fe'lled when the sapwood and medullary rays contain 

 a minimum amount of starch and nitrogenous substances. The 

 least amount of such substances is found immediately after a gre- 

 garious fructification ; in ordinary years, however, soon after the 

 new flush of leaves has come out at the beginning of the season 

 of vegetation. 



The following is merely given as an indication of what might 

 be done in classifying our numerous species according to their 

 power of resisting decay. It must not, however, be forgotten that 

 the conditions in which a piece of wood is placed when used affect 

 to a very considerable extent the question of its durability. For 

 instance, the wood of Ficus reliffiosa decays quickly in the open 

 air, but is extremely durable under water. 



(i). Extremely durabh;. — Teak, Hardwickia hinata, ebony. Aca- 

 cia Catechu, iron-wood, Mesua ferrea, sal. 



(ii). Yery durable. — Deodar, Michelia Champacn, M. excelsa, 

 Dipterocarpus tuberculatus, sundri, black-wood, sissu. 



(iii). Durable. — Albizzia Lehbek and procera, Schima Wallichii, 

 Pteroearpus- spp., oak, Eugenia Jambolana, Terminalia 

 Chebula. 



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