406 



MONTHLY JOURNAL OF AGRICULTURE. 



and well proportioned stem, are far inore 

 prized for cutting into veneers for oi-namental 

 works, on account that the more the bases of 

 the branches are confounded, the more abun-« 

 dant will be the curvatures formed by the de- 

 «cendhig fibres of the buds, and consequently 

 the more beautiful the wood. The celebrated 

 oak of Fairlop, in Hainault forest, Essex, was 

 a pollard of this description ; and a very beau- 

 tiful specimen of its wood may be seen in the 

 reading-desk and pulpit of St. Pancras church 

 in the New Road, north of Loudon. 



To protect the newly forming wood from 

 injury, and prevent the premature conti-ac- 

 tion of the absorbent vessels of the growing 

 buds (which are precisely analogous to the 

 root-fibres of herbaceous plants,) during their 

 progress downward, this process is carried 

 on beneath the bark. In the spring, about 

 the time when the buds of the trees begin to 

 enlarge, the bark readily separates from the 

 last year's wood ; and a viscid secretion, called 

 the cambiuvi, which takes place between the 

 two at that period, is probably the cause of 

 this. It is conjectured that the descending 

 fibres of the buds are nourished by this se- 

 cretion ; and we may even conceive that the 

 ascent of the sap through the woody tubes — 

 tlie first movement of it, at least, after the tor- 

 por of winter has subsided — is occasioned by 

 the stimulus communicated to the vessels in 

 the vicinity of the growing buds, to maintain 

 the flow and supply the continued consump- 

 tion of the cambium. The bark, which in 

 speaking of the first year's shoot was regard- 

 ed as a single integument, is in the ti'unk or 

 older branches a compound of many, accord- 

 ing to the age of the part it covers : a new 

 layer is, indeed, formed annually, coeval with 

 the formation of the new layer of wood ; but 

 the direction of its increase is the reverse of 

 that of the wood, the new matter being inter- 

 nal or immediately surroiuiding the new lay- 

 er of wood. The annual addition to the two, 

 viz. : to the bark and wood — occasions the 

 exterior layers of the former to separate on 

 the trunks of old trees, and either peel off in 

 strips, as in the common birch tree, whose 

 stem looks at a distance as though stiiped with 

 silver, in consequence of the newer bark ap- 

 pearing in the interstices left Ijy the gradually 

 deciduous old one; split into large brittle 

 flakes, as in the plane, leaving the trunk cu- 

 riously mottled with golden yellow ; or, if it 

 still remains attached, it assumes the cracked 

 •and ragged appearance characteristic of that 

 of the elm. Each layer of the bark consists, 

 like the first described as enveloping the new- 

 ly developed shoot, of cellular tissue, the in- 

 terior portion of which is intermingled with 

 woody or tubular tissue ; but as the bark in- 

 creases in thickness, the outer coats gradually 

 lose this regularly organized appearance, 

 ■and become dead matter ; hence the earlier 

 botanists distinguished two separate barks, 

 and considered that each of them was increas- 

 ed by a new annual layer. The outer, really 

 disorganized portion, was denominated the 

 •cortex ; the inner, more rccentlv funned, was 

 (766) 



named the liber, the different coats or succes- 

 sive layers of which, being readily sepai-able 

 in some trees, formed among European na- 

 tions one of the earliest materials used for 

 vi-riting upon, whence the indiscriminate use 

 of the Latin word liber to express a book 

 and the inner bai"k of a tree, the English 

 words bark and book being likewise both de- 

 rivable from the Saxon boc. 



Experiment, which can scarcely be conti'o- 

 verted, proves that the living portion of the 

 trunk of an exogenous tree consists only of 

 the outer layer of the wood and the inner 

 one of the bark, or at least that the preserva- 

 tion of these only is sufficient to maintain the 

 vegetation of the tree where they are of suf- 

 ficient strength to stand alone : the bark, with 

 the exception of the innermost layer, may be 

 wholly removed without checking the vigor 

 of its growth : tlie wood, as may be often 

 seen, may be wholly decayed, with the ex- 

 ception of the outer coats, leaving the trunk 

 a mere shell, which nevertheless puts forth 

 fresh shoots every year, and covers itself with 

 verdure. This is indeed the case, and has 

 been perhaps for many centuries, with trees 

 now standing, of enonnous bulk, especially 

 oaks, and among others that of Salcey ia 

 Northamjitonshire, which some have comput- 

 ed to be more than 1.500 years old. But if 

 an incision be made, of sufficient width to 

 prevent its healing rapidly, round the trunk 

 of a growing tree, so as to penetrate both the 

 bark and the outer circle of the wood, and 

 remove a ring of the latter, its importance is 

 readily demonstrated : if the experiment be 

 made in the early part of the spring, previous 

 to the flow of the sap, the death of the tree 

 or l>ranch inevitably follows. The operation 

 is frequently performed in the back settle- 

 ments of North America, preparatory to that 

 of felling and removing the timber from the 

 land, as the first step toward cultivation ; it is 

 there called girdling, and is done by cutting 

 a complete circle with an ax round the trant 

 of the ti-ee. so as to cut off" all communica- 

 tion of the living wood with the root. Trees 

 thus treated rarely survive beyond the sea- 

 son in which the operation is performed ; but, 

 it is said, there are exceptions, though these 

 may probably be occasioned by unequal or 

 imperfect removal of the woody circle in 

 question. In experiments made in this coun- 

 try upon various trees, I have invariably met 

 with the result above stated : the buds upon 

 the isolated branch have been sometimes de- 

 veloped, or partially so; but, if the wound 

 were sufficiently deep and unifonn, so as to 

 take away a portion all round of the last 

 year's wood, no after-generation of buds took 

 place, although all of the interior layers re- 

 main perfect — proving that the solid timber 

 of a tree has nothing to do with the after- 

 giovvth of it. 



Taking into consideration the mode in 

 which the diametrical increase of die tiimks 

 of exogenous trees take place, viz., the an- 

 nual addition of a layer of wood and of bark 

 between those previously formed, while the 



