20. Wood, whether vascular or fibrous, is however formed, in outlaid plants, first outside of the pith, and then, in shoots of the second year, outside of the wood of the first, and in the third year, outside of the wood of the second; so that supposing the quantity of wood sent down from the growing shoot distributed on a flat plane, the structure in the third year would be as in Figure 27. But since the new wood is distributed all round the stem, (in successive cords or threads, if not at once), the increase of substance after a year or two would be untraceable, unless more shoots than one were formed at the extremity of the branch. Of actual bud and branch structure, I gave introductory account long since in the fifth volume of 'Modern Painters.'[[45]] to which I would now refer the reader; but
both then, and to-day, after twenty years' further time allowed me, I am unable to give the least explanation of the mode in which the wood is really added to the interior stem. I cannot find, even, whether this is mainly done in springtime, or in the summer and autumn, when the young suckers form on the wood; but my impression is that though all the several substances are added annually, a little more pith going to the edges of the pith-plates, and a little more bark to the bark, with a great deal more wood to the wood,—there is a different or at least successive period for each deposit, the carrying all these elements to their places involving a fineness of basket work or web work in the vessels, which neither microscope nor dissecting tool can disentangle. The result on the whole, however, is practically that we have, outside the wood, always a mysterious 'cambium layer,' and then some distinctions in the bark itself, of which we must take separate notice.
21. Of Cambium, Dr. Gray's 220th article gives the following account. "It is not a distinct substance, but a layer of delicate new cells full of sap. The inner portion of the cambium layer is, therefore, nascent wood, and the outer nascent bark. As the cells of this layer multiply, the greater number lengthen vertically into prosenchyma, or woody tissue, while some are transformed into ducts" (wood vessels?) "and others remaining as parenchyma, continue the medullary rays, or commence new ones." Nothing is said here of the part of
the cambium which becomes bark: but at page 128, the thin walled cells of the bark are said to be those of ordinary 'parenchyma,' and in the next page a very important passage occurs, which must have a paragraph to itself. I close the present one with one more protest against the entirely absurd terms 'par-enchyma,' for common cellular tissue, 'pros-enchyma,' for cellular tissue with longer cells;—'cambium' for an early state of both, and 'diachyma' for a peculiar position of one![[46]] while the chemistry of all these substances is wholly neglected, and we have no idea given us of any difference in pith, wood, and bark, than that they are made of short or long—young or old—cells!
22. But in Dr. Gray's 230th article comes this passage of real value. (Italics mine—all.) "While the newer layers of the wood abound in crude sap, which they convey to the leaves, those of the inner bark abound in elaborated sap, which they receive from the leaves, and convey to the cambium layer, or zone of growth. The proper juices and peculiar products of plants are accordingly found in the foliage and bark, especially the latter. In the bark, therefore, either of the stem or root, medicinal and other principles are usually to be sought, rather
than in the wood. Nevertheless, as the wood is kept in connection with the bark by the medullary rays, many products which probably originate in the former are deposited in the wood."
23. Now, at last, I see my way to useful summary of the whole, which I had better give in a separate chapter: and will try in future to do the preliminary work of elaboration of the sap from my authorities, above shown, in its process, to the reader, without making so much fuss about it. But, I think in this case, it was desirable that the floods of pros-, par-, peri-, dia-, and circumlocution, through which one has to wade towards any emergent crag of fact in modern scientific books, should for once be seen in the wasteful tide of them; that so I might finally pray the younger students who feel, or remember, their disastrous sway, to cure themselves for ever of the fatal habit of imagining that they know more of anything after naming it unintelligibly, and thinking about it impudently, than they did by loving sight of its nameless being, and in wise confession of its boundless mystery.
In re-reading the text of this number I can secure my young readers of some things left doubtful, as, for instance, in their acceptance of the word 'Monacha,' for the flower described in the sixth chapter. I have used it now habitually too long to part with it myself, and I think it will be found
serviceable and pleasurable by others. Neither shall I now change the position of the Draconidae, as suggested at p. [118], but keep all as first planned. See among other reasons for doing so the letter quoted in p. [121].