Proserpina Volume II Part 9

Do their walls lengthen laterally when they are empty, or does the 'matiere' inside stuff them more out, (itself increased from what sources?) when they are full? In either case, during this change from circle to hexagon, is the marrow getting thicker without getting longer? If so, the change in the angle of the cells is intentional, and probably is so; but the number of cells should have been the same: and further, the term 'hexagonal' can only be applied to the _section_ of a tubular cell, as in honeycomb, so that the floor and ceiling of our pith cell are left undescribed.

11. Having got thus much of (partly conjectural) idea of the mechanical structure of marrow, here follows the solitary vital, or mortal, fact in the whole business, given in one crushing sentence at the close:---

"The medullary tissue" (first time of using this fine phrase for the marrow,--why can't he say marrowy tissue--'tissue moelleuse'?) "appears very early struck with atony," ('atonic,' want of tone,) "above all, in its central parts." And so ends all he has to say for the present about the marrow! and it never appears to occur to him for a moment, that if indeed the n.o.blest trees live all their lives in a state of healthy and robust paralysis, it is a distinction, hitherto unheard of, between vegetables and animals!

12. Two pages farther on, however, (p. 45,) we get more about the marrow, and of great interest,--to this effect, for I must abstract and complete here, instead of translating.

"The marrow itself is surrounded, as the centre of an electric cable is, by its guarding threads--that is to say, by a number of cords or threads coming between it and the wood, and differing from all others in the tree.

"The entire protecting cylinder composed of them has been called the 'etui,' (or needle-case,) of the marrow. But each of the cords which together form this etui, is itself composed of an almost infinitely delicate thread twisted into a screw, like the common spring of a letter-weigher or a Jack-in-the-box, but of exquisite fineness." Upon this, two pages and an elaborate figure are given to these 'trachees'--tracheas, the French call them,--and we are never told the measure of them, either in diameter or length,[39] and still less, the use of them!

I collect, however, in my thoughts, what I have learned thus far.

13. A tree stem, it seems, is a growing thing, cracked outside, because its skin won't stretch, paralysed inside, because its marrow won't grow, but which continues the process of its life somehow, by knitted nerves without any nervous energy in them, protected by spiral springs without any spring in them.

Stay--I am going too fast. That coiling is perhaps prepared for some kind of uncoiling; and I will try if I can't learn something about it from some other book--noticing, as I pause to think where to look, the advantage of our English tongue in its pithy Saxon word, 'pith,' separating all our ideas of vegetable structure clearly from animal; while the poor Latin and French must use the entirely inaccurate words 'medulla' and 'moelle'; all, however, concurring in their recognition of a vital power of some essential kind in this white cord of cells: "Medulla, sive illa vitalis anima est, ante se tendit, longitudinem impellens." (Pliny, 'Of the Vine,' liber X., cap. xxi.) 'Vitalis anima'--yes--_that_ I accept; but 'longitudinem impellens,' I pause at; being not at all clear, yet, myself, about any impulsive power in the pith.[40]

14. However, I take up first, and with best hope, Dr. Asa Gray, who tells me (Art. 211) that pith consists of parenchyma, 'which is at first gorged with sap,' but that many stems expand so rapidly that their pith is torn into a mere lining or into horizontal plates; and that as the stem grows older, the pith becomes dry and light, and is 'then of no farther use to the plant.' But of what use it ever was, we are not informed; and the Doctor makes us his bow, so far as the professed article on pith goes; but, farther on, I find in his account of 'Sap-wood,' (Art. 224.) that in the germinating plantlet, the sap 'ascends first through the parenchyma, especially through its central portion or pith.' Whereby we are led back to our old question, what sap is, and where it comes from, with the now superadded question, whether the young pith is a mere succulent sponge, or an active power, and constructive mechanism, nourished by the abundant sap: as Columella has it,--

"Naturali enim spiritu omne alimentum virentis quasi quaedam anima, per _medullam_ trunci veluti per siphonem, trahitur in summum."[41]

As none of these authors make any mention of a _communication_ between the cells of the pith, I conclude that the sap they are filled with is taken up by them, and used to construct their own thickening tissue.

15. Next, I take Balfour's 'Structural Botany,' and by his index, under the word 'Pith,' am referred to his articles 8, 72, and 75. In article 8, neither the word pith, nor any expression alluding to it, occurs.

In article 72, the stem of an outlaid tree is defined as consisting of 'pith, fibro-vascular and [42] woody tissue, medullary rays, bark, and epidermis.'

A more detailed statement follows, ill.u.s.trated by a figure surrounded by twenty-three letters--namely, two _b_ s, three _c_ s, four _e_ s, three _f_ s, one _l_, four _m_ s, three _p_ s, one _r_, and two _v_ s.

Eighteen or twenty minute sputters of dots may, with a good lens, be discerned to proceed from this alphabet, and to stop at various points, or lose themselves in the texture, of the represented wood. And, knowing now something of the matter beforehand, guessing a little more, and gleaning the rest with my finest gla.s.s, I achieve the elucidation of the figure, to the following extent, explicable without letters at all, by my more simple drawing, Figure 25.

16. (1) The inner circle full of little cells, diminishing in size towards the outside, represents the pith, 'very large at this period of the growth'--(the first year, we are told in next page,) and 'very large'--he means in proportion to the rest of the branch. _How_ large he does not say, in his text, but states, in his note, that the figure is magnified 26 diameters. I have drawn mine by the more convenient multiplier of 30, and given the real size at B, _according to Balfour_:--but without believing him to be right. I never saw a maple stem of the first year so small.

[Ill.u.s.tration: FIG. 25.]

(2) The black band with white dots round the marrow, represents the marrow-sheath.

(3) From the marrow-sheath run the marrow-rays 'dividing the vascular circle into numerous compact segments.' A 'ray' cannot divide anything into a segment. Only a part.i.tion, or a knife, can do that. But we shall find presently that marrow _rays_ ought to be called marrow-_plates_, and are really mural, forming more or less continuous part.i.tions.

(4) The compact segments 'consist of woody vessels and of porous vessels.'

This is the first we have heard of woody _vessels_! He means the '_fibres_ ligneux' of Figuier; and represents them in each compartment, as at C (Fig.

25). without telling us why he draws the woody vessels as radiating. They appear to radiate, indeed, when wood is sawn across, but they are really upright.

(5) A moist layer of greenish cellular tissue called the cambium layer--black in Figure 25--and he draws it in flat arches, without saying why.

(6), (7), (8) Three layers of bark (called in his note Endophloeum; Mesophloeum, and Epiphloeum!) with 'laticiferous vessels.' [43]

(9) Epidermis. The three layers of bark being separated by single lines, I indicate the epidermis by a double one, with a rough fringe outside, and thus we have the parts of the section clearly visible and distinct for discussion, so far as this first figure goes,--without wanting one letter of all his three and twenty!

17. But on the next page, this ingenious author gives us a new figure, which professes to represent the same order of things in a longitudinal section; and in retracing that order sideways, instead of looking down, he not only introduces new terms, but misses one of his old layers in doing so,--thus:

His order, in explaining Figure 96, contains, as above, nine members of the tree stem.

But his order, in explaining Figure 97, contains only eight, thus:

(1) The pith. (2) Medullary sheath. Circles.

(3) Medullary ray = a Radius.

(4) Vascular zone, with woody _fibres_ (not now vessels!) The fibres are composed of spiral, annular, pitted, and other vessels.

(5) Inner bark or 'liber,' with layer of cambium cells.

(6) Second layer of bark, or 'cellular envelope,' with laticiferous vessels.

(7) Outer or tuberous layer of bark.

(8) Epidermis.

Doing the best I can to get at the muddle-headed gentleman's meaning, it appears, by the lettering of his Figure 97, my 25 above, that the 'liber,'

number 5, contains the cambium layer in the middle of it. The part of the liber between the cambium and the wood is not marked in Figure 96;--but the cambium is number 5, and the liber outside of it is number 6,--the Endophloeum of his note.

[Ill.u.s.tration: FIG. 26.]

Having got himself into this piece of lovely confusion, he proceeds to give a figure of the wood in the second year, which I think he has borrowed, without acknowledgment, from Figuier, omitting a piece of Figuier's woodcut which is unexplained in Figuier's text. I will spare my readers the work I have had to do, in order to get the statements on either side clarified: but I think they will find, if they care to work through the wilderness of the two authors' wits, that this which follows is the sum of what they have effectively to tell us; with the collated list of the main questions they leave unanswered--and, worse, unasked.

18. An ordinary tree branch, in transverse section, consists essentially of three parts only,--the Pith, Wood, and Bark.

The pith is in full animation during the first year--that is to say, during the actual shooting of the wood. We are left to infer that in the second year, the pith of the then unprogressive shoot becomes collective only, not formative; and that the pith of the new shoot virtually energizes the new wood in its deposition beside the old one. Thus, let _a b_, Figure 26, be a shoot of the first year, and _b c_ of the second. The pith remains of the same thickness in both, but that of the new shoot is, I suppose, chiefly active in sending down the new wood to thicken the old one, which is collected, however, and fastened by the extending pith-rays below. You see, I have given each shoot four fibres of wood for its own; then the four fibres of the upper one send out two to thicken the lower: the pith-rays, represented by the white transverse claws, catch and gather all together.

Mind, I certify nothing of this to you; but if this do not happen,--let the botanists tell you what _does_.

19. Secondly. The wood, represented by these four lines, is to be always remembered as consisting of fibres and vessels; therefore it is called 'vascular,' a word which you may as well remember (though rarely needed in familiar English), with its roots, _vas_, a vase, and _vasculum_, a little vase or phial. 'Vascule' may sometimes be allowed in botanical descriptions where 'cell' is not clear enough; thus, at present, we find our botanists calling the pith 'cellular' but the wood 'vascular,' with, I think, the implied meaning that a 'vascule,' little or large, is a long thing, and has some liquid in it, while a 'cell' is a more or less round thing, and to be supposed empty, unless described as full. But what liquid fills the vascules of the wood, they do not tell us.[44] I a.s.sume that they absorb water, as long as the tree lives.

[Ill.u.s.tration: FIG. 27.]

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 quant.i.ty 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 pa.s.sage 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 pa.s.sage 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 circ.u.mlocution, 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.