594 Remarks on MirbcVs Nouvclles Notes. 



circumference. Malpighi conceived that the wood of one year was produced 

 by an alteration of the liber of the preceding season. Duhamel believed that 

 it was deposited by the secretion already spoken of as existing between the 

 bark and wood, and called cambium : he was of opinion that this cambium 

 was formed in the bark, and became converted into both cellular tissue and 

 woody fibre ; and he demonstrated the fallacy of those theories according to 

 which new wood is produced by the wood of the former year. Mr. Knight 

 removed a ring of bark above and below a portion of the bark furnished with 

 a. leaf; and remarked that no increase took place in the wood above the leaf, 

 while a sensible augmentation was observable in the wood below the leaf. 

 Hence an inference is drawn, that the wood is not formed out of the bark as 

 a mere deposit from it, but that it is produced from matter elaborated in 

 the leaves and sent downwards, either through the vessels of the inner bark, 

 along with the matter for forming the liber, by which it is subsequently parted 

 with ; or that it and the liber are transmitted distinct from one another, the 

 one adhering t6 the alburnum, the other to the bark. Mr. Knight was 

 further of opinion that two distinct sets of vessels are sent down, one 

 belonging to the liber, the other to the alburnum; and if a branch of any 

 young tree, the wood of which is formed quickly, be examined when first 

 bursting into leaf, these two sets may be distinctly seen and traced. Take, for 

 instance, a branch of lilac in the beginning of April, and strip off" its bark ; the 

 new wood will be distinctly seen to have passed downwards from the base of 

 each leaf, diverging from its perpendicular course, so as to avoid the bundle 

 of vessels passing into the leaf beneath it : and if the junction of a new branch 

 with that of the previous year be examined, it will be found that all the fibres 

 of wood already seen proceeding from the base of the leaves, having arrived 

 at this point, have not stopped there ; but have passed rapidly downwards, 

 adding to the branch an even layer of fibrous matter or young wood, and 

 turning off at every projection which impedes them, just as the water of 

 a steady but rapid current would be diverted from its course by obstacles in 

 its stream. Now, if the new wood were a mere deposit of the bark, the 

 latter, as it is applied to every part of the old wood, would deposit the wood 

 over the whole surface of the latter, and the deviation of the fibres from 

 obstacles in their downward course could not occur. This, therefore, in my 

 mind, says Dr. Lindley, places • the question as to the origin of the wood 

 beyond all further doubt. Mirbel, continues the doctor, who formerly 

 advocated the doctrine of wood being deposited by bark, has, with the can- 

 dour of a man of real science, fairly admitted the opinion to be no longer 

 tenable ; and he has suggested, in its room, that wood and bark are inde- 

 pendent formations, which is no doubt true ; but, he adds, created out of 

 cambium, in which it is impossible to concur, for this reason. All the 

 writers hitherto mentioned or adverted to have considered the formation of 

 wood only with reference to exogenous trees, and to such only of them as 

 are the common forest trees or plants of Europe. Had they taken into 

 account exotic trees, or any endogenous plants, they would have seen that 

 none of their theories could possibly apply to the formation of wood in that 

 tribe. In endogenous trees there is no cambium, and yet wood is formed in 

 abundance. 



Du Petit Thouars has proposed another theor}'. He maintains that the 

 new zone of wood is neither formed from the cambium, nor from leaves, but 

 from the buds; each individual bud ejects fibrous roots like a seed, and 

 these running down within the bark collectively form the new wood. This 

 theory has met opposition ; and when it is stated that it has been op- 

 posed* by such men as Mirbel and Desfontaines, that is enough to throw 

 it overboard. And yet it has been said that the arguments used by these 

 gentlemen are " undoubted fallacies." Mirbel use fallacies on such a subject ? 

 impossible ! 



The greater part of these observations are extracted from Dr. Lindley's 

 Introduction to Botany, first edition ; and which are presented to show the 



