A Text-book of Paper-making. C. F. Cross
feature in the microscopic diagnosis of lignified fibres and cells. The reagent is prepared by dissolving chlorine to saturation in water. The sodium sulphite solution is prepared by dissolving the crystallised salt in 20 parts distilled water.
Aniline Sulphate Solution.
—With this reagent lignose gives a characteristic deep yellow colouration. A convenient strength is a 2 per cent. solution of the salt. The colour is more quickly developed if the reagent is acidified; a few drops of sulphuric acid should therefore be added.
Solutions of the Aniline Colours.
—Some of these are of importance in enabling the microscopist to differentiate plant tissues. The “affinities” of the fibre substances for these are very various in kind and intensity. The phenomena of staining cannot be adequately treated in our histological scheme, which is necessarily very restricted. We, therefore, merely mention the more important colours which are used in staining, viz., magenta, methylene blue, eosine, diphenylamine blue. A convenient strength is a solution of 1 in 2000. (See also p. 43.)
The employment of the aniline sulphate solution, as well as of the solutions of the aniline colours, presents no difficulties, and therefore needs no detailed description. The former strikes a more or less deep yellow with lignose; the aniline colours stain or dye the tissue or fibre more or less deeply, according to its composition, and, as it is a reciprocal action, {38} according also to the composition of the colouring matter. In following up this subject, the student will require to consult works on vegetable histology.
Preparation of the objects.
—The necessary preliminary to the examination of the fibres themselves is their isolation. This is accomplished either by means of the dissecting microscope, or more roughly, according to circumstances. Having obtained the filaments, they are boiled in a 10 per cent. solution of sodium carbonate until sufficiently softened to yield easily to the “teazing” needles. In certain cases the boiling must be supplemented by trituration in a mortar; this, or some similar operation, is especially necessary when the fibres are embedded in a mass of cellular tissue (parenchyma) e.g. in the fibro-vascular bundles of monocotyledons.
Sections of the filaments are prepared by cutting in a microtome, the filaments being previously agglutinated into a stiff bundle by means of any of the usual stiffening solutions, and after drying, embedded in wax in the usual way. Sections of fresh stems and tissues are cut with a “section” razor.
Having prepared the objects, their examination under the microscope necessarily divides itself into:—(1) the determination of external features; (2) the diagnosis of chemical composition. The fibres themselves will be individually considered in regard to microscopic features.
There is one aspect of these structural features, however, which admits of more general treatment, and in respect to this we may anticipate with advantage, viz., the dimensions or simple elements of form. The importance of the determination of the length and diameter of both filaments and fibres will be readily appreciated by an inspection of the following table, in which the numbers are given for several of the more important.
A careful study of this table in relation to the application of these several fibres, will show that the correlation of the latter with these ultimate dimensions is close and essential. {39}
| TABLE OF LENGTHS OF RAW FIBRES (FILAMENTS) AND DIMENSIONS OF CONSTITUENT CELLS AND FIBRES. | ||||||
| Length of Filament. | Length of Fibres. | Diameter of Cells. | ||||
|---|---|---|---|---|---|---|
| Extreme. | Normal. | |||||
| cm. | cm. | 1⁄100mm. | 1⁄100mm. | |||
| A. Seed hairs. Filaments composed of individual cells. | ||||||
| Cottons. | ||||||
| Gossypium barbadense (Sea Island) | 4·05 | 4·05 | 1·92–2·79 | 2·52 | ||
| Gossypium acuminatum | 2·84 | 2·84 | 2·01–2·99 | 2·94 | ||
| Gossypium arboreum | 2·50 | 2·50 | 2·00–3·78 | 2·99 | ||
| Bombax heptaphyllum | 2–3 | 2–3 | 1·9–2·9 | .. | ||
| B. Bast fibres. Filaments or fibre bundles, made up of individual fibre-cells aggregated together. | ||||||
| Flax. | ||||||
| Linum usitatissimum | 20·140 | 2·0–4·0 | 1·2–2·5 | 1·6 | ||
| Hemp. | ||||||
| Cannabis sativa | 100–300 | .. | 1·5–2·8 | 1·8 | ||
| China Grass. | ||||||
| Boehmeria nivea | .. | 22·0 | 4·0–8·0 | 5·0 | ||
| Ramie. | ||||||
| Boehmeria tenacissima | .. | 8·0 | 1·6 | .. | ||
| Jute. | ||||||
| Corchorus capsularis | 150–300 | ·8 | 1·0–2·0 | 1·6 | ||
| Corchorus olitorius | 150–300 | ·8 | 1·6–3·2 | 2·0 | ||
| Paper mulberry. | ||||||
| Broussonetia papyrifera | .. | ·7–2·1 | .. | 3·6 | ||
| Linden bast. | ||||||
| Tilia grandifolia | .. | 1·1–2·6 | .. | 1·5 | ||
| C. Fibro-vascular bundles | ||||||
| New Zealand Flax. | ||||||
| Phormium tenax | 80–110 | 2·5–5·6 | ·8–1·9 | 1·3 | ||
| Aloe. | ||||||
| Aloe perfoliata | 40–50 | 1·3–3·7 | 1·5–2·4 | .. | ||
| Esparto. | ||||||
| Stipa tenacissima | 10–40 | 0·5–1·9 | ·9–1·5 | .. | ||
A very important point in the diagnosis of a raw material, and next in order of treatment, is the degree of purity of the substance, in so far as this is related to structure. The fibres may be associated with cellular tissue, or with cellular debris, if they have undergone the retting process or other treatment for separation; or with “encrusting and intercellular substances” in various proportions. In the latter case the association with the fibres is usually much more intimate; they are in fact essential constituents of the fibre bundles {40} (bast-fibres, fibro-vascular bundles), whereas the former we may regard as “foreign matter.” We may, however, distinguish between the normal incrustation of the fibre-cells, and such an incrustation of the filaments as would be described as a loose adhesion of non-fibrous matter. The latter is seen in such tissues as the bast of the adansonia, and the fibro-vascular bundles of the aloes. These are points with which observation alone can familiarise the student; as experience grows he will find it increasingly easy to follow general distinctions, and in proportion as he uses his own faculties, so he will be able to generalise for himself. He will find this equally true of the second section of the microscopic examination, i.e., the micro-chemical diagnosis of fibres. Under this head is included the observation of the behaviour of fibres towards the various reagents above described. In addition to their microscopical employment it is useful to note their effect on fibres in the gross, both in their natural state and after treatment with bleaching agents.
In applying the iodine reaction, attention must be paid to the following details of manipulation. Place the object (dry) upon the glass slide, moisten with a few drops of the iodine solution, cover with a glass slip and examine under the microscope. Note the effects, which are those of the iodine alone. Then remove the iodine solution by means of blotting paper, and introduce the sulphuric acid by the method of “irrigation.” The colouration of the cellulose (blue-violet) is immediate; it has the effect moreover, of bringing out more clearly a number of the structural details of the fibre.
We have already treated of the resolution of the raw fibres into cellulose and non-cellulose constituents by processes which convert the latter into soluble derivatives. The student will derive much instruction from following up the attendant structural disintegration with the aid of the microscope. The chemical dissection of lignified fibres by the alternate action of bromine water and alkalis, should be studied by mounting specimens of the fibre at