192 SECTIONAL ADDRESSES 



All that is now left as external evidence of the presence of the branch is 

 the scar where the bark has healed over the stump, and the folds in the 

 bark around this scar where the bark has been thrust outwards against 

 the base of the stem. But within the wood of the trunk, below the scar, 

 the branch stump is left to form a loose knot when planks are cut from this 

 region because of the way the wood of the branch has simply been gripped 

 in the flanks of the vertically running fibres of the wood of the main stem. 

 Still further within the tree the branch wood has more continuity with the 

 wood of the trunk, but still remains a tapering, radially directed 

 cone with its fibres, in the main, running radially inwards, distinct 

 from the downwardly running fibres of the main axis. This is 

 particularly clearly shown when the wood of the main axis rots away 

 leaving the tapering branch end pointing into the hollow centre of the 

 trunk. 



In the hardwood, the beginnings of radial growth similarly wait upon 

 apical growth, but the branching is less mathematical in its regularity 

 and there is no constant succession of longer and larger branches regularly 

 spaced along the axis. Usually radial growth is proceeding at the same 

 time on main stem and branch stem and a continuous layer of wood is 

 laid down smoothly on all sides of the branch-base, in closest continuity 

 with the wood of the main axis. Here again however, if light does not 

 reach them, lateral branches lower on the tree will fail to make any 

 extension growth ; radial growth will then also fail in them and these 

 branches will dry and die. Then successive increments of wood upon 

 the main axis will thrust against the bark where it is held tight around the 

 bases of the dead dry branches, and thus ultimately strip the lower part 

 of the trunk of such branches, the stumps of which will promptly be 

 buried under the new layers of wood, with only the branch scars and their 

 attendant folds in the bark as evidence of their presence. When these 

 stumps are brought to light as knots in planks they will usually be very 

 firm because of the different manner in which wood of branch and main 

 axis made union, and because under high forest conditions the lateral 

 branches die and fall off young, leaving no dead stub of wood to be buried 

 in the wood of the main axis. Only when older branches have been cut 

 off by the forester in such a manner as to leave projecting stumps are these 

 likely to be buried and reappear as loose knots in the planks cut from the 

 trees. 



Although the hardwood has not the mathematical regularity of branch- 

 ing characteristic of the softwood, its branch system is usually built 

 up upon an ordered plan. The case of poplar may be described as 

 an interesting example in which, as in oaks, the natural abscission of 

 branches contributes to the rapid simplification of the branch system. 



The vigorous vegetative seasonal shoot of a poplar bears many buds, 

 of which the terminal one normally makes very vigorous growth the follow- 

 ing season. The next few buds remain dormant. Then follow a group 

 of buds which grow out into vegetative shoots, the uppermost of these 

 usually being the stronger and the lower ones progressively weaker until 

 again buds are reached which remain dormant. Cambial activity in these 

 various shoots shows some proportionality to their vigour of growth ; in 



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