GROWTH OF TKEES. 24/ 



trading like the new shoot of the spring and autumn, and draw- 

 ing out like a telescope. This is the manner in which the wood 

 vessels increase ; the bark vessels are rather ditFerent, as I shall 

 explain at another opportunity. But this is not all which is 

 of consequence to the subject— the retiring of the bark-vessels The retiring 



to make way for the new row of alburnum is managed in various ^'^'^^ °^ ^^^ 



J. ° bark. 



»vays m diiterent trees. In most fruit trees the bark-vessels 



bend up, receding from the part the alburnum is to occupy, 

 and then pushing out towards the rind, and thus increasing the 

 circle. In forest .trees the smaller cross vessels break away, and 

 leave all the circular ones to retire towards the rind. But 

 whichever way they act, I have a specimen which elucidates 

 each fact, and makes it beyond contradiction : and it may easily 

 be seen, that constantly taking the cutting of a branch every 

 season from the same tree, its increase, and the manner of it, 

 must be exactly noted : but it sometimes happens, that the 

 season is unfavourable, and that the severity of the weather so 

 checks the sap that should form the new row of alburnum in 

 March, that it rises not sufficiently to deposit so large a semicir- 

 cle 'j then the old remains on that side, and causes that appear- 

 ance sometimes found in wood, which presents the yearly circle 

 incomplete ; but it occurs not often, especially in indigenous trees. 

 Nature performs her part too perfectly, unless we make her 

 fail by removing various trees and shrubs from a more favour- 

 able climate to our own — then I have seen it produce a strange 

 ejfect. I have many specimens, in shrubs particularly, where 

 the pith has been wholly on one side, almost joining the bark, 

 though twenty or thirty circles, well defined, have shown three 

 quarters of the year 5 but the winter quarter has been as void, 

 as if it should never have had a mark— this must be wholly 

 owing to its missing its spring shoots, from the coldness or 

 damp of our climate. The exact nianner, in which every 

 branch in a tree tells its own age, is also a curious fact. I have 

 before observed, that the trunk of a tree shows exactly how 

 long it has been planted, but the branch shows only the seasons 

 it has grown, one row for each year. I have taken a whole 

 tree in this manner, examining each division j and the exact 

 way in which it answers to the time of its shooting is curious 

 to see — the autumn shoot, however, is so much wider than 



the 



