ANATOMY. 11 



period of growth, the deeper, moister and more full of nutri- 

 ment the soil, the greater the amount of light to which the 

 crown of the tree is exposed and of available material from 

 which the wood is constructed; — the wider the annual zone. 

 The most important factor here in the breadth of the annual 

 zones of wood is the amount of light received by a fully- 

 developed crown, as may be at once seen from the broad 

 annual zones of standards over coppice, or of reserved trees 

 left standing after a felling in densely-grown high forest. It is 

 not uncommon, in the latter case, to find that the annual 

 zones of standards increase two- or three-fold, provided the soil 

 has not deteriorated owing to the removal of the other trees in 

 the wood. 



Damp years favourable to vegetation yield a larger wood- 

 increment and, consequently, broader annual zones than dry 

 years, and warm, damp years greatly increase the width of the 

 zones of summer-wood. A short period of growth, damage 

 by frost (especially in the case of delicate species), a large 

 production of seed and insect-attacks, reduce the width of the 

 annual zones.* 



[Some annual zones are 1 to H inches wide (poplars, willows and 

 some tropical trees, especially Bomhax Malabaricum), whilst in some 

 trees from 30 to 60 annual zones may occur in an inch of radius. In 

 branchwood the zones are usually narrower, and in rootwood always 

 narrower, than in stems. — Tr.] 



(c) Uiiiformiti/ of the Annual Zones. 



As a rule, annual woody zones are broader in young trees than 

 in old ones ; they therefore become smaller from the centre out- 

 wards, even while the sectional area of the zone may remain 

 constant. The pith of a tree is frequently excentric, the reason 

 for this being the different width of the annual zones on opposite 

 sides of the stem. This may go so far that a zone may be 

 appreciably present on one side of a tree only, tapering-off quite 

 finely at both ends on the other side. The good quality of 

 timber is more prejudiced by periodical inequality of the annual 

 zones than by this peculiarity. The occurrence of annual zones 



* R. Hartis, Iiifiuence of Seed- Years on Wood-Increraout. Frst. u. Jfrtlztiis. 



