351 



counteracting the influence of gravitation, when nccdlul, and that ii 

 does not constitute the sole, or even the principal agent of nature in this 

 business. If gravitation were the sole cause of giving a direction to 

 roots, it might be asked, why roots select the best soil in descending, 

 which they arc well known to do 1 Because, if acted on only by gra- 

 vitation, they would have no choice but to descend, unless prevented by 

 some obstacle that could not be surmounted. Such an obstacle might 

 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 taproot of the oak, about which so much has been said, Du- 

 hamel 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 taproots ; 

 and that as both, at the mature age of the plants, uniformly lose their 

 preeminent character, so they arc not only analogous to, but coexistent 

 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 taproots to their 

 place in phytology. See Thomson's An. of Philos. Vol. XIII. p. 252. 



Note V. Page 131. 



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

 more important than pruning, it may be worth wlule 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 eradicate 

 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 olT, 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 ail, 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 eftectiiig that purpose, much judgment, and some 



