FORMATION OF WOOD. 61 



the wood and bark, as cambium cells; and, in Endogens, are developed 

 in the internal parts of the stem. Proof seems, however, still wanting 

 of the direction in which the development of wood takes place in the 

 former; while, in the latter, observations seem to be in favour of a 

 vertical formation, or of additions of woody fibre being made in a 

 downward direction, as in roots, thus following the course of the 

 descending elaborated sap.* 



117. The formation of wood depends mainly on the functions of the 

 leaves being carried on properly, and this can only be effected by ex- 

 posure to air and light. The more vigorously the plant grows, the 

 better is the wood produced. Experiments made in the British dock- 

 yards 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, bore a greater weight than a similar 

 plank of slow- grown oak. 



118. In order that trees may grow well, and that timber may be 

 properly formed, great care should be taken in planting at proper 

 distances 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, while 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 a por- 

 tion of them is subsequently removed, the remainder is easily blown 

 over by the wind. In thick plantations, it is only on 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 subse- 

 quent 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 properly planted and 

 thinned, little pruning is required. 



* For full details relative to the formation of wood, see Gaudichaud, Recherches sur 1'Organo- 

 graphie, &c., Paris, 1841 ; Mirbel, Annales des Sciences Naturelles, 3d series, torn, xx., &c. ; Nau- 

 din, do., 3d series, torn. i. ; Henfrey, Annals of Natural History, 2d series, vol. i. 



