Fig. 323.
A. Cotton; B. Fibres of Flax; C. Filaments of Silk; D. Wool of Sheep.
The fibrous tissue of plants is of great value in many manufactures. It supplies material for our linens, cordage, paper, and other industries. This tissue is remarkable for toughness of fibre, and exhibits an approach to indestructibility, in the use it is put to in connection with the electric light. It is of importance, then, to be able to distinguish it from other fibres with which it is often mixed in various manufactures. Here the use of the microscope is found of considerable importance. In flax and hemp, in which the fibres are of great length, there are traces of transverse markings at short intervals. In the rough condition in which flax is imported into this country, the fibres have been separated, to a certain extent, by a process termed hackling, and further subjected to hackling, maceration, and bleaching, before it can be reduced to the white silky condition required by the spinner and weaver, and finally assumes the appearance of structureless tubes, [Fig. 323] B. China-grass, New Zealand flax, and some other plants produce a similar material, but are not so strong, in consequence of the outer membrane containing more lignine. It is important to the manufacturer that he should be able to determine the true character of some of the textures employed in articles of clothing; this he may do by the aid of the microscope. In linen we find each component thread made up of the longitudinal, unmarked fibres of flax; but if cotton has been mixed, we recognise a flattened, more or less rounded band, as in [Fig. 323] A, having a very striking resemblance to hair, which, in reality, it is; since, in the condition of elongated cells, it lines the inner surface of the pod. These, again, should he contrasted with the filaments of silk, [Fig. 323] C, and also of wool, [Fig. 323] D. The latter may be at once recognised by the zigzag transverse markings on its fibres. The surface of wool is covered with furrowed and twisted fine cross lines, of which there are from 2,000 to 4,000 in an inch. On this structure depends its felting property, in judging of fleeces, attention should be paid to the fineness and elasticity of the fibre—the furrowed and scaly surface, as shown by the microscope, the quantity of fibre in a given surface, the purity of the fleece, upon which depend the success of the scouring and subsequent operations.
Fig. 324.
1. Woody Fibre from the root of the Elder, exhibiting small pores; 2. Woody fibre of fossil wood, showing large pores; 3. Woody fibre of fossil wood, bordered with pores and spiral fibres; 4. Fossil wood from coal.
In the mummy-cloths of the Egyptians flax only was used, whereas the Peruvians used cotton alone. By the many improvements introduced into manufacturing processes, flax has been reduced to the fineness and texture of silk, and even made to resemble other materials.
Fossil Plants.—It is well known that the primordial forests furnish a number of families of plants familiar to the modern algæologist. The cord-like plant, Chorda filium, known as “dead men’s ropes,” from its proving fatal at times to the too adventurous swimmer who gets entangled in its thick wreaths, had a Lower Silurian representative, known to palæontologists as Palæochorda, or ancient chorda, which existed, apparently, in two species,—a larger and a smaller. The still better known Chondrus crispus, the Irish moss, or Carrageen moss, has likewise its apparent, though more distant representative, in chondritis, a Lower Silurian algal, of which there seems to exist at least three species. The fucoids, or kelpweeds, appear to have also their representatives in such plants as Fucoides gracilis, of the Lower Silurians of the Malverns; in short, the Thallogens of the first ages of vegetable life seem to have resembled in the group, and in at least their more prominent features, the algæ of the existing time. And with the first indications of land we pass from the thallogens to the acrogens—from the seaweeds to the fern-allies. The Lycopodiaceæ, or club-mosses, bear in the axils of their leaves minute circular cases, which form the receptacles of their spore-like seeds. And when high in the Upper Silurian system, and just when preparing to quit it for the Lower Old Red Sandstone, we detect our earliest terrestrial organisms, we find that they are composed exclusively of those little spore-receptacles.
The existing plants whence we derive our analogies in dealing with the vegetation of this early period contribute but little, if at all, to the support of animal life. The ferns and their allies remain untouched by the grazing animals. Our native club-mosses, though once used in medicine, are positively deleterious; horsetails (Equisetaceæ), though harmless, so abound in silex, which wrap them round with a cuticle of stone, that they are rarely cropped by cattle; while the thickets of fern which cover our hill and dell, and seem so temptingly rich and green in their season, scarce support the existence of a single creature, and remain untouched, in stem and leaf, from their first appearance in spring until they droop and wither under the frosts of early winter.