78 FORMATION OF WOOD. 



matter depends mainly on the functions of the leaves being car- 

 ried on properly, and this can only be effected by exposure to air 

 and light. The more vigorously the plant grows,, the better is the 

 wood produced. Experiments made in the British dockyards proved 

 that those oaks which had formed the thickest zones yielded the best 

 timber. Barlow's experiments . at Woolwich showed that a plank of 

 quick-grown oak withstood a greater strain than a similar plank of 

 slow-grown oak. The stumps of fir-trees sometimes exhibit a circle of 

 woody tissue which has been formed after the trees have been cut 

 down, and without the agency of leaves. In some cases the vigour of 

 these stumps has been traced to the roots being grafted into those 

 of adjoining trees bearing branches and leaves. 



In order that trees may grow well, and that timber may be pro- 

 perly formed, great care should be taken in planting at proper dis- 

 tances, and in soil fitted for the trees. Firs ought to be planted from 

 6 to 8 feet apart ; and hardwood trees, for a permanent plantation, 28 

 feet distant, the spaces being filled up with larch, spruce, or Scotch 

 fir, according to soil and situation. Hardwood is of no value till it 

 has attained some age, whOe larch and spruce may be applied to use 

 in ten or twelve years ; and thus judicious thinning may be practised. 

 When trees are set too close their leaves are interrupted in their 

 functions ; many of them fall off, leaving the stems bare ; the wood 

 is imperfectly formed, and the roots are not sent out vigorously. 

 When such plantations are allowed to grow without being thinned, 

 the trees are drawn up without having a hold of the ground ; and 

 when some of them are subsequently removed the remainder are 

 easily blown over by the wind. In thick plantations it is only in 

 the trees next the outside, where the leaves and branches are freely 

 formed, that the wood and roots are properly developed. When a 

 tree is fully exposed to air and light on one side only, it is frequently 

 found that the woody zones on that side are largest. When trees are 

 judiciously planted, there is a great saving both in the original outlay 

 and in the subsequent treatment. Pruning, or the shortening of 

 branches, and the removal of superfluous ones, ought to be cautiously 

 practised. It is only applicable to young branches and twigs ; and is 

 had recourse to chiefly in the case of fruit-trees, when the object is to 

 make the plants produce flowers and fruit. If forest trees are pro- 

 perly planted and thinned, little pruning is required. 



