28 



HISTORr OF THK VEGETABLE KINGDOM. 



genninate. Its aerial evolution gives rise to a 

 scion, or young branch; while from its base, 

 that is, from tlie point by which it adheres to 

 the parent plant, proceed fibres, which the 

 author compares to the radicle of the embryo, 

 and which, gliding along in the moist layer of 

 cambium, between the liber and alburnum, de- 

 scend to the lower part of the vegetable. Now, 

 in their course downwards, these fibres meet 

 those which descend from other buds, unite witli 

 tham, and thus fonn a layer more or less thick, 

 which acquires consistence and solidity, and 

 fonns each succeeding year a new woody layer. 

 The liber, when once formed, does not change 

 its nature, or undergo any transformation. 



This theory is extremely ingenious, and the 

 author adduces sevei-al facts in proof of its ac- 

 curacy. Thus, he says, when a strong circular 

 ligature is applied to the tninl< of a dicoty- 

 ledonous tree, a swelling or rim is formed above 

 the obstacle, and no growth in diameter takes 

 place below the ligature. This swelling is 

 formed by the woody fibres which descend from 

 the base of the buds, running in the cambium 

 situated between the liber and alburnum. These 

 woody fibres meet an obstacle which they are 

 unable to surmount, are stopped, and accumulate 

 there. Henceforth no new woody layers can be 

 formed beneath the ligature, as the fibres of which 

 tjiey are formed cease to ai-rive there. Such is 

 the explanation given l)y M. Du Petit-Thouars of 

 the phenomena presented after the application 

 of a ligature, which most authors account for in 

 quite a different manner. 



He farther adduces, in support of his theory, 

 the phenomena exhibited in consequence of the 

 act of grafting. In grafting by inoculation, it 

 is usual to take a bud which is yet stationary, 

 and apply its base to the layer of cambium 

 which has been laid l)are. After this the radicles 

 or fibres which proceed from the base of the 

 bud, glide between the bark and alburnum, and 

 the new stock is thus identified with that on 

 which it has been grafted. 



As a confirmation of this fact, this botanist 

 has had in his possession a branch of Rohinia 

 psetidacada, on which has been grafted a young 

 scion of Robinia hisjnda. The stock died, but 

 the graft having continued to vegetate, there is 

 seen proceeding from its base a mass formed of 

 very distinct fibres, which embrace the extremity 

 of the branch to a considerable extent, and form 

 a kind of sheath for it. In this example, it is 

 perfectly clear that the fibres descend from the 

 base of the graft to spread over the stock. 



Notwithstanding all the ai'guments brought 

 forward by tlie author in defence of his theory, 

 it has not as yet been entirely adopted by any 

 physiologist. On the contrary, almost all authors 

 who treat of vegetable physics have in some de- 

 cree opposed it. The principal arguraenta that 



have been brought against it are the following : 

 l.rf. It has been said that there is no incontrover- 

 tible proof that the fibres which establish a com- 

 munication between the buds and the stem* 

 which support them, descend in the manner 

 alleged from these buds to the roots. To this, 

 however, our theorist replies, that the buds are 

 indeed the source, the first origin, of the woody 

 fibres, but that they do not furnish all the ma- 

 terials of the elongation of these fibres ; for when 

 the latter have once emerged from the base of 

 the buds, they are found to be immersed in the 

 cambium, where they absorb all that is neces- 

 sary for their growth. 2dlp, It has been objected 

 that the phenomena of the circular swelling 

 which forms after a ligature has been applied to 

 the trunk, may be accounted for by the inter- 

 ception and stagnation of the descending sap. 

 But, says Du Petit-Thouars, the experiment of 

 Hales, which was confirmed by Du Ilamel, af- 

 fords a refutation of this objection : Two cylin- 

 ders of bark having been completely insulated 

 by the removal of three rings, one of the cylin- 

 ders being furnished with a bud, while the other 

 had none, the result was that a circular swelling 

 formed on the first cylinder only, thus affording 

 an evident proof that the buds give rise to the 

 woody fibres. Sdly, It is impossible to conceive 

 how fibres so slender as those which unite the 

 buds to the stems could, in a space of time so 

 short as that during which the stem grows in 

 diameter, descend, by their proper weight, from 

 the summit of a tree sixty or eighty feet high 

 to its base. As the opinion of the learned aca- 

 demician is not that the fibres issue and descend 

 ready formed from the base of the buds, but, 

 on the contrary, that they form as they pass 

 through the layers of cambium, this objection 

 requires no refutation. 4iM!/, That, since the 

 woody layers are formed of the fibres which de- 

 scend from the base of the buds, if, in grafting 

 by inoculation, a bud taken from a tree having 

 coloured wood, is grafted upon an individual 

 having white wood, the fibres which proceed 

 from this bud ought to retain their colour, and 

 the new woody layers which they form ought 

 to be similarly coloured ; but this is not the case. 

 This objection, which has been considered as 

 one of the strongest that have been adduced, 

 our author finds little difficulty in refuting, it 

 having originated in a misconception of the 

 author's ojiinion. In fact, as Du Petit-Thouars 

 has constantly stated, the filjres coming from 

 the base of the bud are nourished by the cam- 

 bium of the branch at whose surface they are 

 formed. Now, in the case of grafting with two 

 trees, the wood of which is differently coloured, 

 so long as the new fil)res are immersed in the 

 cambium of the piece that has coloured wood, 

 they retain their natural tint ; but, when they 

 are formed at the expense of the cambium of 



