CHEMICAL AND MICROSCOPICAL INVESTIGATIONS. 
9 
and from atmospheric influences, there are seen exuding from the surface of the wood, gelatinous 
protuberances, mamelons , as they were named by Duhamel, or gelatinous drops, as they were called by 
Meyen.* These productions, after they have become multiplied in number, and extending nearer to each 
other, at length become hardened and organized as fresh bark. Duhamel looked upon this as an 
organizable liquid. Meyen noticed that this exudation, from the first moment when it shewed itself at 
the extremity of the medullary rays, was composed of a very delicate cellular tissue, the cells of which 
contained a gummy mucilage ; but M. Trecul first clearly showed that these new productions are from the 
beginning composed of cells, and that these cells, which have a gelatinous appearance, are produced by those 
of the generative layer ( couche generatrice ), which remains on the surface after the bark has been removed. 
It would seem, indeed, that where these have been removed by the abrasion of the whole surface of the 
wood, renewal of the bark does not take place. It will be seen how strongly these views confirm the 
practical value of the plan of MTvor.f 
W e have seen that the one special condition of renewal is that the surface of the denuded wood should 
be constantly kept moist. In the year 1852 M. Trecul submitted to the Academy the trunk of a tree 
(. Ngssa angulisans ) brought from Louisiana, where it had been protected by the shade of a damp, marshy 
forest from the direct action of the sun. It had been deprived of its bark for the space of sixteen or 
seventeen inches all round the stem, and nevertheless not only continued to grow, but bore leaves and 
fruit. ITesh layers had begun to form, not only in connection with the bark both above and below the 
decorticated portion, but also on the surface of the wood deprived of its bark. Oblong or hemispherical 
projections covered with bark of a greyish colour, having as yet no contact with the remaining bark of 
the tree, grew as represented in the accompanying Plate. Well-executed representations of microscopical 
sections of these renewed portions are added. This formation appears to be connected with prolonga- 
tion of the medullary rays, and, in addition to a fibro-vascular structure, there are seen, as in the 
Plate No. 18,j; some punctuated and radiated vessels. The projections themselves partake of the nature 
of wood rather than bark, in this respect differing from the perfect bark obtained by mossing. 
Origin of the Renewed Barit. 
As it seems to be demonstrated that the most profitable mode of cultivation will be the renewal of the 
bark under moss, as described above, it becomes a very important practical question to consider whence 
the fresh and very rich materials are derived out of which the new bark is elaborated. 
In order to arrive at the truth in this matter, it is necessary to pass in review some ascertained 
facts in reference to the course of those fluids in the plant, by means of which it is nourished and increased. 
It is through the roots, which are continually extending, and, as it were, going in search of nourishment, 
that the plant absorbs from the soil a large quantity of water and of common air, — both of which are 
needful to its existence. It also receives various earthy salts, of which it appears, from the most recent 
research, to have the power of admitting some and rejecting others. § As is well expressed by Grew 
in his ‘Anatomy of Plants’ (Book i. p. 15), “The contiguous moisture, by the cortical body, being a 
body laxe and spongy, is easily admitted ; yet not all indiscriminately, but that which is more adapted to 
pass through the surrounding cuticle.” The liquid thus absorbed by the roots rises through the fibro- 
vascular system. It is an- essentially watery liquid, and contains only traces of certain principles, — gum, 
* I liave not met with, any chemical analysis of this organizable matter, but suspect, from imperfect experiments of my own, 
that hydrate of silica (in some soluble form) plays an important part in it. 
f Mr. Broughton writes (March 16, 1868) : — “ I have long remarked that the bark, when carefully removed without injury 
to the cambium, quickly renews itself from below, not from the edges. The analysis made of bark so renewed, of six months' growth, 
has at present corroborated your statement respecting the old practice of the cascarilleros." J Sciences Nat. Botanique, 1852. 
§ See a very interesting paper, “ De la Repartition de la Potasse et de la Soude dans les Vegetaux," lu par M. Peligotin, a 
l'Academie des Sciences, le 4 novembre 1867, 'Annales de Chimie et de Physique.' 
D 
