330 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



THE PHYSIOLOGY OF PRUNING. 

 By E. A. Bunyard, F.R.H.S. 

 [Read September 14, 1909.] 



The study of pruning has exercised the minds and pens of horticulturists 

 from very early days, and a vast literature, which almost threatens to 

 overwhelm the student, has sprung up around the subject. 



France has contributed perhaps more than her full share to this vast 

 collection, and no French pomologist of note has considered his life well 

 spent until he has seen his name upon a title-page beneath the words 

 "L'Art de Tailler." England has treated the subject more as a matter 

 of dogma, with results generally practical, often contradictory. The 

 student is thus bewildered by the manifold sources of information and 

 hesitates between the theorist — meaning here, as often, the man who 

 writes a book — and the practical man — he who does not. 



To students in this case I would recommend a study of plant 

 physiology or plant functions as the only sure basis upon which a 

 knowledge of correct pruning can be founded. A short consideration of 

 the vital processes of plants will, I think, demonstrate how much the 

 pruner may learn from the physiologist. 



Let us consider first the functions of the roots. Eoots absorb water 

 from the soil by means of root-hairs, small but extremely delicate 

 outgrowths from the fibres. The main and hard root branches cannot 

 absorb water through their bark, as this strong protective tissue is 

 too corky and dense to permit it to pass. The water absorbed by the 

 root-hairs contains all the inorganic salts required by the plant, an 

 important point to which reference will be made later. This salt- 

 laden water is then forced upward by root-pressure, a fact which may be 

 observed when a large tree is cut down and the stump and roots left 

 intact. When the sap begins to flow in spring it streams in large 

 quantities from the stump. Root-pressure is due to the fact that the 

 root-hairs are distended with much water, while the inner cells of 

 the root are less full ; the water therefore flows in the line of least 

 resistance. The roots and branches of the tree are thus so many 

 aqueducts or water-pipes conveying the water supply to the leaves and 

 fruits. An examination of a stem of any plant will show, however, that 

 there are many tubes or channels through which liquids can flow, and 

 they can be divided into two systems, the inner and outer. These tubes 

 are, however, not continuous, as a water-pipe, but are elongated cells 

 closed at each end, and the liquid soaks through them in a manner which 

 is described below. 



The water which is forced from below is conveyed by the inner series 

 of tubes, a fact which can be demonstrated by taking a small ring of bark 

 from a woody stem, such as a pear branch, taking care that the incision 



