the Age of Trees from, the number of Rings. 453 



the appearances in it are illustrated by Mr Mann in Plate 

 IV. Fig. 2 shows the characteristics of a well-marked ring, 

 the fifth. The somewhat gradual flattening or apparent 

 compression of the latest autumn wood of the fourth year 

 (a) into a circle forming a distinct line of demarcation is well 

 shown, and the larger size of the cells of the spring wood of 

 the fifth year (b), particularly at the very commencement, is 

 noticeable. The differences, however, in density of tissue and 

 size of lumina are not nearly so well marked as is ordinarily 

 the case in the wood of temperate climates. In fig. 3, which 

 shows the demarcation between the first and second year's 

 growth, the comparative feebleness of the characteristics are 

 seen; and it may be remarked that in other parts of this 

 ring, as well as in other true rings both of Acacia mollissiraa 

 and Acacia lo'phantha, the band of flattened cells almost, if 

 not entirely, disappears. Fig. 4 shows the very slight differ- 

 ences between the older tissue {a) and the younger (b) in a 

 false ring. 



Thus we have a transition from the well-marked annual 

 ring of the fifth year, through the feebly-marked annual ring 

 of the first year, to the almost insensible impress of a seasonal 

 variation — all, no doubt, due to the influence of varying 

 degrees of heat or moisture, or both combined. And if 

 these results occur in a climate with a well-marked summer 

 and winter season, we are at no loss to account for the con- 

 fused and numerous rings noted by Sir Eobert Christison in 

 tropical wood. His observations, however, were only with 

 the naked eye, and it is much to be desired that the nature 

 of the wood-rings in tropical dicotyledons should be thoroughly 

 investigated by aid of the microscope. 



Taking a general review of the results, the following 

 conclusions may be drawn : — 



1. The ages of the specimens cannot be determined with 

 certainty by counting the rings on the blocks, except in 

 Eobinia. In Melia, zones of wood, sharply defined by lines 

 of demarcation similar to those met with in our British trees, 

 are seen, but the zones exceed in number the years of age of 

 the tree. In the Acacias a series of wave-like rings greatly 

 surpass in number the years of age of the trees, and it is 

 difficult or impossible to pick out the true demarcation of 

 the yearly growths. 



