SUITED FOR PLANTING. • 279 



Mild loamy soil, iu which sand aud lime are present in a 

 higher degree than clay, deep, fresh, and rich in vegetable 

 mould, is favourable to the growth of many forest trees, such as 

 oak. Lime is best suited for beech [Fagus sylvatica), Ash (Fraxmus 

 excelsior), Maples (^cc?-). Elms {Ulmus), black or Austrian Pine 

 {Pinus austriaca), Dwarf Pine (Finus 'pnmiilio, seu Muglms), and 

 Yew [Taxus haccata). As already remarked, a hinding clay, 

 without a sufficient percentage of humus, is not suitable for any 

 forest trees. In the heat of summer it contracts, bursts asunder, 

 and injures the rootlets. A soil composed of quartz sand, with a 

 small percentage of clay, fresh and rich in humus, is capable of 

 nourishing sufliciently any tree occurring in our island, if it is not 

 too shallow. Soils that are rich (minerally), although they yield 

 trees of superior height and greater cubic content, if they are very 

 moist, produce timber of inferior quality and less durability. 



Dry and arid soils, if properly treated, are, as a rule, capable 

 of nourishing the Scotch fir [Finus sylvestris), along with which 

 the birch — a soft wood — (Bctula verrucosa), might be grown if 

 advisable. Por example, in the North German plain, where the 

 pine forests are cut through by railways, safety Ijelts are planted 

 with birches to prevent sparks from the engine funnel reaching 

 the tinder-like leaves that cover the soil. 



5. The quantity of Humus contained m a Soil plays an important 

 part in regard to the growth of trees, for by the decomposition of the 

 leaves, carbon and various chemical compounds forming the ashes 

 are returned to the soil. Carbonic acid, formed by the decom- 

 position of humus, affords indispensable nourishment to trees, 

 and decomposes such minerals as occur, so that they become 

 soluble in water, and are absorbed by the rootlets in the form of 

 alkalies. Humus also absorbs from the atmosphere ammonia 

 (NHg), oxygen, moisture, &c., all substances necessary for the 

 nourishment of plants. It possesses in a high degree the power 

 of absorbing and retaining moisture, and as it is only moderately 

 binding, it renders more loose and porous a binding, clayey soil, 

 and binds a loose sandy one. 



6. The Nature of the Subsoil affects the quantity and quality of 

 the timber produced, seeing that it materially affects the quantity 

 of moisture contained in any soil. It may be impervious or cleft, 

 in horizontal, inclined, or tilted layers. Subsoils of plastic clay, 

 of moorpan (Ortstein and Easeneisenstein of the North German 

 plain), or of quartz conglomerate, are the most unfavourable ; far 

 more suitable are loams, marls, or peats (when the latter is not 

 too wet), and such rocks as are moderately cleft, by reason of 

 which the upper soil can only be moderately moist. 



(&) Concerninj the Situation of the Soil, — We must consider 

 I. Pleiiiht above the level of the sea. 



