Cellulose and Amylaceous Particles Under Iodine

tissue were seen the first dissolving reactions finishing the effect of the tincture of iodine; the cellulose became gradually divided into groups of amylaceous particles, which gave a beautiful violet-coloured outline to the cylindrical cells radiating or spread out symmetrically from the points of insertion of each joint.” [Boox 1, BOOK I. ORGANOGRAPHY ; OR, OF THE STRUCTURE OF PLANTS. CHAPTER I. OF THE ELEMENTARY ORGANS. Tr plants are considered with reference to their internal organisation, they appear at first sight to consist of a vast mul- titude of exceedingly minute cavities, separated by a mem- branous substance; more exactly examined, it is found that these cavities have a variety of different figures, and that each is closed up from those that surround it ; if the inquiry is carried still farther, it will be discovered that the partitions between the cavities are all double, and that by maceration in water, or by other methods, the cavities with their enclosing _ membrane may be separated from each other into distinct bodies. These bodies constitute what is called Vegetable Tissue, or Elementary Organs: they are the Similary parts of Grew. The organic basis of the elementary organs is called cellulose, a ternary compound, derived from cambium or organic mucus, a viscid azotised quaternary secretion, which occurs everywhere in young parts, and as a residuum in old parts. This organic mucus, or cambium, is also named, by Vegetable Physiologists, oryanisable matter. . Organic mucus has long been known asa substance exist- ing in Algals, prior to the appearance of organisation, as in Protococcus nivalis, &c. It has been found by Brongniart, Henslow, &c. in the form of cuticle, a thin homogeneous STRUCTURE, ] ORGANIC MUCUS—CAMBIUM. x membrane, applied.to the surface of the leaves of some plants, and only separable after maceration ; it is probable that it constitutes the whole exterior coating of all plants; it is cer- tainly drawn over the sacs which constitute hairs ; 1 have found it distinctly on the petals of Hydrotenia Meleagris (see Bot. Reg. 1838: misc. No. 128), but its extreme tenuity and firm adhesion to the tissue below it renders it difficult to detect it; and there is no doubt that it occurs very generally in the interior of plants between their cells, filling up the intercellular spaces, and gluing together all the parts. Mohl, with his usual skill, has shown that this substance is found so frequently, that we cannot refuse to acknowledge its presence as a constant fact. The Box, and the young annual shoots of Sambucus nigra, are especially noticed as well suited to show this structure ; it will be seen to form a considerable part of the mass of the albumen of Alstromeria Salsilla, see fig. 2. c. where it is 5!,; of an inch in diameter. Valentin has measured the thickness of the intercellular organic mucus in several instances, and gives the following table of the pro- portion between it and the cells of certain plants, calculated in Paris inches. Thickness of the Size of Proportion of the intercellular mucus, the esll. — Ast to the Sud. Camellia japonica. . 0,000112 00006751: 6,02 Hoya carnosa . . . 0,000150 —0,000650 1 Magnolia grandiflora . 0,060150 —0,000425 1 Cestrum laurifolium —.0,000275 ~——0,001550 1 Daphne Laureola . . 0,000390 00010001: Pinus Picea . . —. 0,000450 = 0,001200S 1 Aloe intermedia. . . 0,000775 ~—0,002100S 1 Aloe Lingua. . —. 0,000825 0,0 1: Agave americana . . . 0,000850 —0,002375 1 Meyen admits the fact of the presence of this intercellular mucus, and considers it a secretion from the sides of the cells. He particularly refers to its condition in the petiole of Beta cycla, in proof of the correctness of that view. No doubt can be entertained that it is of universal occur- rence between the cells or tubes of all vegetable fabrics. Cambium, as it is called, originally observed at the sepa- ration of the bark and wood of Exogens, in the spring, seems 8 CAMBIUM—-MEMBRANE AND FIBRE. [woox 1. to be nothing more than this universally distributed organic mucus. An account of its composition and of the part which it plays in the Vegetable Organisation, has been given by Mirbel and Payen, (Comptes rendus, 1843, i. 98 ; Annales des Sciences Nat., xix. p. 193). They describe this substance, which precedes the appearance of cells, and is always present where vegetable matter is in a state of growth, as containing substances analogous to those which constitute animal bodies, that is to say, including nitrogen. It is, however, also mixed with other materials not azotised, composed of carbon and the elements of water, such as dextrine, gum, starch, sugar, glycose, mannite, &e. At the moment when vegetation is renewed by the development of cells, unazotised cellulose also appears, and increases by new layers, identical in their chemical constitution, although sometimes other matters are added to form woody tissue. From this kind of thickening of cellulose, we can understand, say our authors, why wood in the: interior of stems contains little nitrogen, while spon- gioles, buds, and growing ovules, contain from ten to twenty times as much. It may be, however, that, as Link says, the word cambium is applied by Payen and Mirbel to secretions essentially different, and that much more refined chemical analysis is required to show that all intercellular or orga- nisable matter is identical in composition. It is the opinion of some anatomists that of membrane and fibre, the latter only is the basis of the tissue of plants: fibre itself being a form of membrane ; or, which there is no sufficient evidence to show, that all membrane is composed of fibres interlaced. But we find both the one and the other developed in many of the most imperfectly organised plants, such as Scleroderma and other fungals, and it is difficult to conceive how that can be a mere modification of membrane which can be generated independently of it, which has no external resemblance to it, and which in most cases is obviously something superadded. Link observes that Mohl has taken great pains to refute Meyen’s assertion, that the vegetable membrane is formed of spiral fibres. But in reality the assertion had only a very limited application, because by far the greatest number of membranes in the STRUCTURE. ] ELEMENTARY MEMBRANE. 9 vegetable kingdom do not exhibit such a composition. Link never could find the spiral structure described by Meyen in the aerial roots of what he calls a Stelis. It is, however, very remarkable, as Link observes, “that many portions of plants have a tendency to split spirally; this, however, only takes place in the thicker parts ; for instance, in old porous vessels, and even in bark, as in that of the birch tree. We need not, therefore, go back with Mohl to a molecular theory, which is better left to the ‘philosophers’ of nature.” (See p. 13.) Membrane, as true cellulose, may be regarded as being in the beginning a gelatinous precipitate from the organic mucus of vegetation. Like all such precipitates, it must be understood to be a collection of globular molecules adhering by their points of contact ; and hence its permeability. The history of organic precipitates has been studied by both Harting and Link, of whom the latter thus states the result of his observations :—“ All precipitates, when analysed imme_ diately after their formation, exhibit globules; these globules unite themselves to larger ones (being therefore fluid, like globules of quicksilver) ; and these united globules or drops, subsequently only (and that frequently under our own eyes) change themselves into crystals. If M. Harting did not observe this, it was owing to his not having examined the precipitates speedily enough. The globules sometimes form flat surfaces, sometimes they are gelatinous. All fluid sub- stances exhibit a commencement of solidity on their surface— for we attribute fluidity to a substance, if the parts can be displaced from each other by the slightest application of force ; and this can ouly be done, when the attracting and repelling powers of the homogencous parts neutralise each other, which cannot be the case on the surface of fluid sub- stances, where the parts are unequally drawn in different directions. This solidity increases with the surface, and a thin stratum of fluidity is consequently in itself solid. The degree of solidity certainly depends on the degree of attrac- tion among the parts, which, as is well known, is different also in fluid substances, as exhibited by quicksilver and water. Nothing, therefore, is required for the production of a 10 ELEMENTARY MEMBRANE—PROTOPLASM. [Book 16 membrane, but the separation ofa stratum of fluidity—as every bubble shows. The half fluid substances, mucus, jelly, &c., are a mixture of solid and fluid parts, as can be seen when they are dried.” Membrane varies in its degree of transparency, being occasionally so exceedingly thin as to be scarcely discover- able, except by the little particles that stick to it, or by its refraction of light, but in ferns, some fuci, and other cryp- togamic plants, it is brown from its first birth: according to Roper it is green in Viscum album : Link says it is green in the leaves of Ruellia Sabiniana and the petiole ‘of Cycas revoluta; and Meyen mentions its being orange-coloured in the petiole of many tropical Orchids. It is always excessively thin when first. generated ; arid whatever thickness it afterwards agquires must be supposed to be owing to the incorporation or incrustation of secreted matter. This was first observed by Mohl in Palm-trees, where he found a successive addition of strata to the lining of the cavities of the cells; and is apparently an universal occurrence where membrane becomes thickened. But the matter added to membrane is often so homogenous as to offer no trace of its being deposited concentrically, even when examined by the most powerful microscopes, and I am not always able to discover the regular lines upon its section which are represented so uniformly by the German anato- mists. It is, however, plain enough that the membrane of the woody tubes of the liber is in many plants thickened successively by the deposit inside of concentric layers of sedimentary matter, as may be seen in Castanea vesca (fig. 1. a), and Betula alba, and in the cells below the stomates of Pinus sylvestris (fig. 1. 5); and there are sufficient traces of it to be found elsewhere to justify the opinion that it is a common mode of increment in thickness. The first layer of matter is invariably soft and azotised, and now bears the well-contrived name of protoplasm, proposed THICKENING PROCESSES. 11 strvctURE.] SCLEROGEN- by Professor Mohl. Turpin has remarked that the thicken- ing of the membranous sides of cells by means of a hard sedimentary matter, called by him Selerogen, is what causes the grittiness of the pear, and the boniness of the stone of the peach and plum, inall which the osseous parts were originally ‘membranous. It is, however, by no means in old or woody parts alone that a thickening of the membrane takes place: it may be observed distinctly in the cells of the corolla of Convolvulus tricolor, and in fact occurs in all parts con- taining fluid matter exposed to vital action. Moh] and others are of opinion that all addition to the thickness of vegetable membrane takes place on its inner face; but the universal presence of a cuticle overlying the outer series of cells-in every organ exposed to air, and the granulations found on the outside of old hairs (see Elements of Botany, fig. 67), render it difficult to deny the increment of membrane in thickness on both sides. This view has more especially been taken by Harting and Mulder, who conclude from chemical evidence, that in the development of cell- membrane, all the layers which in a full-grown cell have a peculiar chemical reaction not occurring in the young mem- brane, have been formed subsequently to that membrane, which consists entirely of cellulose ; and that since such layers occur on the outside of full-grown cells (the innermost layer of which is composed of cellulose, and therefore corre- sponds to the membrane of the young cell), the cell-membrane must have increased in thickness in consequence of a subse- quent -deposition, from within outwards, of layers having a different chemical constitution. Mohl has discussed this opinion with his usual sagacity. “Let us examine,” he says, “whether these conclusions may not be too hasty. It does not admit of the slightest doubt, that the chemical compounds which are coloured yellow by iodine and sulphuric acid, and which characterise the outer and intermediate layers of most full-grown cells, are of later origin than the cellulose which forms the membrane of the young cell. From this fact, how- ever, it is a great leap to the assumption, that those layers which are composed of a substance differing from cellulose, are in reference to their situation also newly-formed layers, 12 THICKENING PROCESS. [poo 1. such as are wanting in young cells. That is certainly pos- sible; but it is also possible, that the fact as shown by anatomy is altogether otherwise. With the same kind of reason as that which leads to the inference that a new layer is formed externally, we may assume that in a cell originally consisting of true cellulose, that substance subsequently, and without any alteration of its relative position, is absorbed and replaced by an essentially different chemical compound ; or that cellulose remains and a new compound is depo- sited between its molecules, interfering with the behaviour of cellulose towards iodine and sulphuric acid. Such an infiltration might occur without any visible thickening of the layer, either if it were not in very great abundance, or if the growth of the membrane in a lateral direction, in consequence of the expansion of the cell, were to make room for the deposit of a considerable quantity of some foreign compound. In these cases, the possibility of which no one will call in question, a layer would indeed be formed altogether new in a chemical aspect, but no alteration in anatomical relations would appear: and from such a chemical transformation no conclusion should be drawn as to the order in which the dif- ferent layers of the cell-membrane originate ; because such metamorphoses may take place as readily in the last as in the first formed layer. If we admit the possibility of such a metamorphosis, it must also be conceded that the chemical reaction of any particular layer affords no sure means of recognising it as a peculiar anatomical layer; for it may be casily imagined, that in different cells, the layers corresponding to each other in an anatomical point of view, may exhibit a great distinction in regard to their chemical transformations. Until well-grounded experience has taught us which of the cases, that have here been mentioned as possible, really occwrs in nature, we can only allow ourselves to be guided, in the recognition of the different layers and the deter- mination of the order in which they make their appear- ance, by their anatomical relations; and although in very many cases the influence of chemical re-agents affords an excellent means by which we are enabled to distinguish the individual layers of cell-membrane, which without this structure.] APPARENT FIBROUS STRUCTURE—PORES, 13 assistance it would be difficult or impossible to recognise, yet in availing ourselves of such assistance we must keep the anatomical relations constantly in view. The study of these relations leads, I believe, to a result diametrically opposed to that maintained by Mulder and Harting. (See Annals of Natural History, vol. xviii., p. 265, for further details.) Elementary membrane generally tears readily, as if its component atoms did not cohere with greater force in one direction than another; but I have met with a remarkable instance to the contrary of this in Bromelia nudicaulis, in which the membrane of the cuticle breaks into little teeth of nearly equal width when torn. (Plate I. fig. 6.) The same circumstance has been remarked by Dr. Willshire in Til- landsia usneoides. (Ann. Nat. Hist. xviii.) Hence it may be conjectured, that what we call primitive membrane is itself the result either of primitive fibres completely consolidated, or of molecules originally disposed in a spiral direction, as Raspail supposes. (Chim. Org. p. 85.) In the membrane of certain plants, as in the liber of the Oleander, in Vinca minor, and others belonging to the families of Dogbanes (Apocynacez) and Asclepiads, an appearance is discoverable of spiral steep ascending lines, some of which turn to the right, others to the left, thus dividing the surface into a number of minute rhomboidal spaces. Mohl, however,-who has made this observation, does not therefore consider with Grew that the membrane is woven together of fibres, but that their appearance is owing to a small difference in the thickness of the cellular membrane: “Perhaps a different arrangement of the molecules at various points, perhaps a small difference in the thickness of the membrane, causes a different refraction of light, precisely in the same way as fibres are visible in badly melted glass.” Valentin confirms Mohl’s views, and regards such appearances as caused by the process of ligni- fication. Schleiden goes further, and maintains that all the deposits to which the thickening of membrane is owing have originally a spiral direction. (See p. 9.) Membrane is in all cases, when first formed, destitute of visible pores; although, as it is readily permeable by fluids, it must necessarily be furnished with invisible passages. An 14 SUPPOSED PORES ARE PITS. [Book 1. opinion to the contrary of this has been held by some bota- nists, who have described the existence of holes or pores in the membrane of tissue, and have even thought they saw a distinct rim to them; but this idea, which originated in imperfect observation with ill-constructed glasses, is now generally abandoned. (See p. 16.) Different explanations have been given of the supposed pores. Dutrochet asserted them to be grains of matter sticking to the membrane: he found that boiling them in hot nitric acid rendered them opaque, and that treating them with a solution of caustic potash restored their trans- parency,—a property incompatible with a perforation. But the so-called pores operated upon by this observer were particles of some secreted matter sticking to the membrane. Slack believed them to be, in other cases, thin spaces in the sides of tissue, such as might be produced by the adhesion and separation at regular intervals of a thread developed spirally within a membranous sac. (Z'rans. Soc. Arts, xlix.) A nearly similar opinion was previously offered by Mohl, who considers the dots on the membrane of tissue to be thinner portions of it. He says it may be distinctly seen by the aid of a powerful miscroscope that the little circles which are visible on the surface of the tissue of Palm-trees are passages (meatus) in the thickness of the membrane, opening into the cavity of the cells, and closed externally by the membrane itself. He adds, that when dotted tissue is in contact, these passages are placed exactly opposite to each other. (Martius Palm, Anat. v. col. 2). To the latter cause is undoubtedly owing the general appearance of dots, as has now been ascer- tained by repeated observations. If a thin section of any vessel or cell, the sides of which appear to be dotted, is placed under a good microscope, it will be found to have the matter deposited on its sides pierced with short passages, which give the appearance of dotting, because the sides of the membrane are thinner where they are stationed than anywhere else. (See Plate II. fig. 2.) They are therefore not dots, but pits. Should the young observer fail in-seeing the pits in their natural state, the applic