and the Means of ascertaining it. 109 



On an inspection of these figures, we will find, that trees at 

 advanced periods of life continue to form layers which do not 

 yield in thiclcness to those of a moderate age ; that each species, 

 after increasing rapidly in youth, seems at a certain age to grow 

 at a regular rate ; that, in short, we can give a tolerable expla- 

 nation of such a difference, by supposing that at an early period, 

 i. e. before fifty or sixty years, the roots and branches of forest- 

 treee not being embarrassed by those near them, increase at 

 liberty, but on exceeding this age that they do not grow so 

 much, because they encounter the roots or branches of their 

 neighbours ; that the cause of inequalities in growth, is general- 

 ly owing, either to the middle root of the tree meeting layers of 

 good or bad soil, or because at certain periods the tree, being 

 disincumbered of its neighbours, is able to grow at more 

 liberty. 



Similar tables of a great many species, and of individuals of 

 each species, would afford excellent evidence of the progress of 

 vegetation. First, we might be enabled to establish in every 

 species its average increase annually, and thus, on finding out 

 the circumference of an exogenous tree, we might discover its 

 age almost to a certainty ; and it should be observed that the 

 principal differences occur during the first century; and that 

 afterwards its growth is more uniform. Secondly, A knowledge 

 of the average growth and solidity of one kind of wood being 

 attained, we could form an opinion of the layers of each trunk 

 by their thickness, if it depart less or more from the qualities 

 peculiar to its species, We may thus be certain, that the oak 

 No. 1. in the table is very inferior to those of Nos. 2. and 3, 

 because the thickness of its layers is too great for the wood to 

 have acquired its proper degree of hardness. Thirdly, If the 

 law which I suggest be correct, that at a certain age (sixty to 

 eighty years in oak-trees), every tree ceases to grow so rapidly, 

 and progresses more regularly, me might deduce precise rules 

 as to the period when we should fell certain trees. I therefore 

 presume to believe, that tables of horizontal cuts would be of 

 peculiar advantage, and I recommend their preparation to tra- 

 vellers, and those who live near extensive clearings of woods or 

 dock-yards. 



2. If we are unable to g-et a transverse section of trunks, 

 there is another mode of judging of their growth, viz. to find 

 out old individuals of each species, the date of which is known, 

 to measure their circumference, to deduct from that, their aver- 

 age increase, and make use of it in calculating the age of other 

 trees of the same species, always keeping in view, that, local 

 circumstances excepted, the average taken of a younger tree 

 always gives a result too great for the increase, or too small for 

 the age of old trees. I read in Evelyn, that a Daiic, called 



