BENEFITS OF PRUNING. 249 



by the act of thinning. The sap does not flow in 

 one class of vessels only, but in several ; not in longi- 

 tudinal ones only, but transverse ones as well. Each 

 branch and limb evidently has a primary class of 

 longitudinal sap-vessels peculiarly its own for convey- 

 ing its nourishment, but in addition to these there is a 

 secondary class of transverse ones, all connected one 

 with another, and with every part of the tree to its 

 remotest extremities. This is clearly demonstrated by 

 cutting off a branch and leaving the smallest ligature 

 on the outer surface along with the bark, which is 

 found sufficient to keep the whole branch supplied 

 with sap alive for an indefinite length of time ; or 

 what is still more remarkable and illustrative of the 

 affinity of sap-vessels and their connection one with 

 another, is the experiment of cutting down a tree 

 of any size, small or great, and leaving the slightest 

 connection of the sap-wood entire at the root. By 

 this means I have seen a beech- tree of large size kept 

 alive for many years, and no part of it suffer decay, 

 not even the extremities of the branches, notwithstand- 

 ing that the sap-vessels through which the whole struc- 

 ture of the tree was nourished and supplied with sap 

 were not over 4 inches by 1 J inch, including the bark. 

 Trees in this state of prostration, and with the limited 

 supply of sap, do not make any perceptible enlarge- 

 ment either in shoots or woody substance ; but the 

 circumstance of their budding, foliating, and defoliating 

 the same as other trees, shows conclusively that the 

 sap becomes common throughout the whole structure 

 of the tree, and though entering by a small channel 

 and only a limited number of vessels, it soon spreads 

 into other channels, and extends uniformly to all parts 

 of the tree. 



