406 Thinning, Pruning, and Girdling Trees. 



may, generally, be observed in so short a space of time as to leave 

 no possible doubt upon the subject ; whilst, on the other handy 

 the growth of all trees is comparatively so slow, as to require 

 much longer time, and a series of close observations of the effect 

 of experiments, before any satisfactory deductions can be ob- 

 tained. By such experiments it may, probably, be made to ap- 

 pear, that, to a certain extent, the removal of any tree will have 

 the effect of ultimately adding to the bulk of its neighbour, io 

 much more than the amount of the solid contents of that which 

 has been taken away ; though, without such process, neither of 

 tliem would have attained to one quarter of the bulk of the tree 

 which was left. 



Pruning Trees. — Experiments may be still more available 

 for showing the effects of pruning, or (if there are any who, in 

 defiance of Mr. Pontey, are bold enough to pursue the plan) of 

 not pruning at alL Sir Henry Steuart, in a note to his Planter'' & 

 Guide, says that Pontey's Forest Primer has done more injury, 

 as well as more good, to the woods of Great Britain, than any 

 work that has appeared within a century. The evidences of the 

 injury which it has done are but too visible, without anything 

 like close examination, in numerous instances ; but, whether 

 it has ever done any substantial good may, perhaps, be ques- 

 tionable, when the subject is investigated without prejudice, and 

 with some consideration of those discoveries respecting the pro- 

 cesses of vegetation of which Pontey was manifestly ignorant when 

 be wrote. All his notions are resolvable into the idea, that the 

 feeding sap of trees proceeds only in an upward direction ; 

 whereas the observations of Mr. Knight and others clearly show 

 that the upward progress of the sap contributes but little, com- 

 paratively speaking, to the growth of the tree ; and that it is 

 chiefly by the downward passage of the juices, after they have 

 been altered in their nature in the leaves, that the increase of 

 growth is effected. 



From these considerations, and also from the visible structure 

 of trunks and branches when they are longitudinally divided, it 

 i& apparent, that every trunk and branch is fed as much by the 

 branches that pass into it, as by the roots, if not more ; and, if 

 any trees (not having been pruned) are subjected to the experi- 

 ment of measuring the girt of the trunk, and also of the prin- 

 cipal branches, it will be generally found, that the joint contents 

 of the sections of those branches, taken according to the usual 

 method of measuring timber by what is called quarter girt 

 (that is, by dividing the circumference into 4, and multiply- 

 ing the produce, or \, into itself), will approach very nearly to 

 that of the trunk. Thus, suppose a tree having two branches only 

 proceeding from the main stem, and the circumference of a in 

 Jig. 63. to be 8 in. ; this being squared, as the common phrase is 



