FORMATION OF WOOD 269 



-In evergreens there are rarely distinct .annual 

 rings and tlie reason is not hard to find. Ever- 

 greens do not shed all their leaves at one time ; 

 there is, with them, no period of absolute 

 quiescence. True, elaboration of food, trans- 

 piration and all the various functions of the 

 leaf are not carried on so vigorously in the 

 winter as in the summer, but there is never 

 the perfectly dormant period which we find in 

 the deciduous trees. 



In the evergreens of temperate regions this 

 slowing up of the plant activities does cause 

 some differences of structure between the autumn 

 and spring wood, but the activities of the 

 tropical evergreens are equally pronounced the 

 year through, so that even a semblance of an 

 annual ring may be. sought in vain. The relation- 

 ship between the structure of the wood and the 

 nature of plant foliage is very striking and no 

 less important. 



The number of annual rings to the inch varies 

 considerably according to the position in the 

 tree, there being fewer in the centre than towards 

 the outside, or conversely in the centre of a 

 tree the annual rings are wider than they are 

 nearer to the surface, and this is important to 

 the timber merchant for, in conifers at any rate, 

 the smaller the proportion of the soft spring 



