August 28, 191 3] 



NATURE 



<>77 



the country ; but examples of over-pruning are almost 

 as general, and are to be found in most private gar- 

 dens, where the stunted trees throw out every year 

 thickets of twigs, serving no other purpose than that 

 of feeding the bonfire. 



Besides the annual branch-pruning there are other 

 operations included under the term pruning, but the 

 only one to which 1 can now allude is root-pruning. 

 In this the roots are unearthed and cut back, with 

 the view of increasing the fruitfulness of the tree. 

 The check which such an operation gives to the 

 growth is very severe, and if carried to excess, will 

 kill the tree entirely. It is evidently one which should 

 b<- undertaken only in very exceptional circum- 

 stances, such as where the tree is showing rampant 

 growth, and will neither flower nor fruit. We hear 

 little of root-pruning except in private gardens, and 

 we should scarcely ever hear anything of it there if 

 a more rational system of branch-pruning were 

 adopted. When the branches are cut away to an 

 excessive extent, the balance between branch and root 

 can only be restored by cutting the roots away too. 

 But to injure the tree in one way, and to attempt to 

 correct matters by injuring it in another way, is not 

 a very intelligent procedure. 



Passing to the problems connected with the trans- 

 planting of a tree; during this operation many of the 

 old root-tips are torn off in lifting the tree, but others 

 are killed by becoming dried up on exposure to the 

 air. Some exposure is always inevitable, and in most 

 cases several days elapse between the lifting and the 

 planting of a tree. It is of great importance, how- 

 ever, that this exposure should be reduced to the 

 narrowest limits. A number of trees were lifted at 

 Woburn, and some of them were replanted at once, 

 whilst others were left in a shed for four days before 

 doing so, and it was found that the latter made only 

 four-fifths as much growth as the former during the 

 following season. It is on this account that plant- 

 ing trees in the spring should be discountenanced, as 

 drying winds are then more prevalent ; but if this 

 drying effect is avoided, it is immaterial when the 

 planting is carried out : similar trees planted at 

 different times between November 28 and March 3 

 were found to do equally well. 



Much stress is always laid by horticulturists on the 

 importance of selecting trees with a good supply of 

 fibrous roots, and of taking the utmost care of these 

 roots, spreading them out, and shaking the earth 

 lightly between them. But such precepts are based on 

 ignorance as to the principles of root-growth. Nine- 

 tenths of these roots have lost their tips, they are 

 useless, and as good as dead, for they certainly will 

 die in a very short time. Anyone can satisfy himself 

 on this point; it is only necessary to mark a few of 

 these roots by tying strands of silk round them, and 

 on lifting the tree again at the end of the season 

 it will be found that the rootlets have all, or nearly 

 all, died, and that in their place a new svstem of 

 rootlets has arisen from the thicker portions of the 

 older roots. In fact, we have found that 

 trees do better if the smallest of the fibrous 

 roots are removed before planting, and also if all the 

 roots are shortened to a certain extent. The reason of 

 this is, not only that it is well to remove parts of the 

 tree which are bound to die, but that the new root- 

 lets which form will be more vigorous if they originate 

 from the thicker portions of the old roots, where the 

 store of material for their nourishment is greater. 

 The practice of leaving the roots as long as possible, 

 and carefully trimming their ends, is quite a mistaken 

 one, for the ends of these roots, having lost the root- 

 tip, cannot start into growth again, and it has been 

 found that of the new rootlets which originate, only 

 some 15 per cent, arise from the neighbourhood of 

 NO. 2287, VOL. 91] 



the ends of the old roots, the rest originating from 

 higher up towards the stem, or even from the stem 

 itself. 



Two other conclusions may also be drawn from 

 what has been mentioned, namely that it can make 

 little or no difference to the future welfare of the tree 

 whether the ends of the old roots are trimmed, or 

 left jagged and torn as they are when removed from 

 the nursery, nor whether these roots are carefully 

 spread out in the ground, instead of being huddkd 

 into the hole prepared for them; for it is the new 

 rootlets which are to be formed, and not the old 

 ones, on which the future life of the tree depends. 

 Both these conclusions have been verified by actual 

 experiment. Even when the roots were twisted and 

 tied together in a bundle, the tree did just as well as 

 when they were spread out in the orthodox fashion. 



It is thus seen that all these practices which are 

 supposed to be essential to the proper planting of a 

 tree are really immaterial, and, in fact, that the 

 violation of them within certain limits is beneficial. 

 But the benefit was not sufficient to explain certain 

 results which we obtained, and which puzzled us for 

 many years. We had made a plantation in which, by 

 way of demonstration, the trees had been planted in 

 violation of all the accepted canons, and we expected 

 that these trees would afford an awful lesson to the 

 careless planter. But instead of that, they flourished 

 rather better than their carefully planted neighbours. 

 The results were naturally set aside as accidental, 

 and a repetition, and subsequently many repetitions, 

 were made ; but the roughly planted trees refused to 

 behave badly, and flourished so much more than their 

 neighbours that they often showed two or three times 

 more growth than these did. The principal cause of 

 this was eventually traced to the fact that the soil 

 round these trees had been heavily rammed at the 

 planting, instead of being shaken over the roots and 

 merely pressed down. When we consider that the 

 welfare of the transplanted tree depends on its sending 

 out new rootlets from the old roots, it is evident that 

 anything which brings the soil into intimate contact 

 with these roots will be beneficial, and ramming the 

 soil down, especially if it is in a wet condition at the 

 time, will do this more effectually than could ever be 

 done by the gentler method of planting. These some- 

 what surprising results, therefore, receive a simple 

 explanation, and it is easy to satisfy ourselves, by 

 lifting the trees at the end of a year, that the rammed 

 trees have actually formed more new roots than those 

 carefully planted. Such novel methods of planting 

 naturally excited the wrath of horticulturists, who, as 

 a body, are inclined to carry the veneration for tradi- 

 tional procedure to excess, and we were careful to 

 obtain overwhelming evidence as to the facts before 

 publishing our results. Some seventy sets of experi- 

 ments were made, in which about 2000 trees were 

 used ; the soils in which the trees were planted being 

 of everv variety, and situated in eight different coun- 

 ties. Naturally, the results varied, but the average 

 of them showed that ramming might be expected to 

 increase the growth of the tree by nearly 50 per cent., 

 during the first or first two years, at any rate in 

 heavy or fairly heavy soils. In a light sandy soil it 

 naturally had "no effect, for the obvious reason that, 

 by the time the tree started into growth, any con- 

 solidation of the soil caused by the ramming would 

 have disappeared. In one case only were the results 

 of ramming very bad, and that was in the London 

 clay, where the absence of aeration caused sulphuretted 

 hydrogen to be developed. In other clay soils, no such 

 results ensued (the Woburn farm itself is on the 

 Oxford clay). 



That trees will not flourish unless the soil in which 

 they are growing is sufficiently aerated, is well known. 



