SECTION IV. 



407 



indeed stop them, or turn them aside, but it could not make them grow 

 upwards, or ascend a bank, as they are also known to do in search of 

 food. 



As to the tap-root of the Oak, about which so much has been said, 

 Duhamel asserts its existence, and Mr Knight denies it ; but from my 

 own experience, I am forced to agree with the former writer. I think 

 that, as stated in the text, a striking resemblance is found to exist 

 between the leading branches of this and several other trees and their 

 tap-roots ; and that as both, at the mature age of the plants, uniformly 

 lose their pre-eminent character, so they are not only analagous to, 

 but co-existent with each other. For an examination of Mr Knight's 

 theory as to gravitation, I refer the curious reader to a paper on that 

 subject by Mr Keith, author of Physiological Botany, which is full of 

 learning and ingenuity, and serves, in my opinion, fully to restore tap- 

 roots to their place in phytology. See Thomson's An. of Philos. voL 

 xiii. p. 252. 



Note V. Page 97. 



As there is no process in the whole range of arboricultural economy 

 more important than pruning, it may be worth while to say something 

 on it in this place. Pruning may be said to embrace the five following 

 objects : first, to advance the growth and bulk of trees ; secondly, to. 

 reduce or lessen their bulk ; thirdly, to modify or alter their form" ; 

 fourthly, to renew their decayed parts ; and fifthly, to cure and eradi- 

 cate the diseases to which they are subject. 



Of these the most important, and, till of late years, certainly the least 

 attended to, is the first ; as the ultimate value of the wood in most 

 cases depends upon it, and the actual weight of the timber produced. 

 With all deciduous trees cultivated for profit, the art is to cut off, at an 

 early age, the weak and superfluous lateral shoots, so that the portion 

 of sap employed in their nourishment may be thrown into the strong 

 ones ; and above all to direct a proper portion of the ligneous matter of 

 the tree into the main stem or trunk, and thereby generate clean and 

 sound timber. But in effecting that purpose, much judgment and some 

 science are requisite ; because, as branches are just as necessary to the 

 nourishment of the tree as roots, (namely, in elaborating by means of 

 their leaves, and carrying down to the stem the descending sap,) so, if 

 they be retrenched to excess, the nourishment of the tree must be 

 checked ; or it may happen, although you succeed in advancing the 

 hulk of the wood, that you may very sensibly deteriorate its quality^ 

 and consequently its value. 



With a view to establish a proper system of pruning, Mr William 



