The textile fibres; their physical, microscopical, and chemical properties

Preface

The present book, it is hoped, will be of assistance to both the practical operator in textiles and the student on textile subjects. It has been the outgrowth of a number of years of experience in the teaching of textile chemistry, as well as practical observation in the many mill problems which have come under the notice of the author.

The textile fibres form the raw materials for many of our greatest industries, and hence it is of importance that the facts concerning them should be systematized into some form of scientific knowledge. The author has attempted, however, not to allow the purely scientific phase of the subject to overbalance the practical bearing of such knowledge on the every-day problems of industry. -*

Heretofore, the literature on the textile fibres has been chiefly confined to a chapter or two in general treatises on dyeing or other textile subjects, or to specialized books such as Hohnel's work on the microscopy of the fibres. It has been the author's endeavor, in the present volume, to bring together, as far as possible, all of the material available for the study of the textile fibres. Such material is as yet incomplete, and rather poorly organized at its best; but it is hoped that this volume may prove a stimulus along the several lines of research which are available in this field. Unfortunately, the subject of the textile fibres has been lamentably neglected by chemists, although there is abundant indication that a fertile field of research is open to chemists in this direction, and such work would have not onlv a scientific value, but might also lead to great industrial worth. There is, as yet, relatively little known concerning the chemical iv PREFACE.

constituents of the fibres, and the manner in which varying chemical conditions affect the composition and properties of these constituents. The action of various chemical agents on the fibre as an individual has been but very imperfectly studied. More work has been done in the microscopical field concerning the properties of the fibres; but even here, the knowledge is very incomplete and disjointed, and especial attention is drawn to the fact there is yet a large amount of work to be done in the microchemistry of the subject.

The author has endeavored to emphasize throughout this Volume the importance of the study of the fibre as an individual, for in many cases it is misleading to assume that the behavior of the individual fibre is identical with that of a large mass of fibres in the form of yarn or cloth. In the latter case, the difference in physical condition and the action of mechanical forces has an important influence. By going back to the study of the individual fibre as a basis, many explanations can be given which could not be discovered otherwise.

It is hoped that this book may afford instruction both to the manufacturer and to the student; assisting the former in solving some of the many practical problems constantly occurring in the manufacture of textiles, and urging the latter on to an increased effort in the scientific development of the subject.

J. Merritt Matthews.

Philadelphia Textu-e School, August, 1904.

Chapter I. Page

Classification of the Textile Fibres i

I. Fibres Chiefly Used for Textiles. 2. Animal and Vegetable Fibres. 3. Mineral and Artificial Fibres.

CHAPTER n.

Wool and Hair Fibres 5

I. Wool and Hair. 2. Physiology and Structure of Wool.

Chapter XV

I. Jute. 2. Ramie or China-grass. 3. Hemp. 4. Sunn Hemp. 5. Ambari or Gambo Hemp. 6. New Zealand Flax. 7. Manila Hemp. 8. Sisal Hemp. 9. Aloe Fibre or Mauritius Hemp. 10. Pita Fibre. II. Pineapple Fibre or Silk-grass. 12. Coir Fibre.

CONTENTS. vu

Chapter XVI. Page

I. Introductory. 2. Qualitative Tests. 3. Distinction between Cotton and Linen. 4. Distinction between New Zealand Flax, Jute, Hemp, and Linen. 5. Ligneous Matter. 6. Goodale's Table. 7. Systematic Analysis of Mixed Fibres. 8. Identification of Artificial Silks. 9. Distinction between True Silk and Different Varieties of Wild Silk. 10. Micro-analytical Tables.

Chapter XVII

I. Wool and Cotton Fabrics. 2. Wool and Silk. 3. Silk and Cotton. 4. Wool, Cotton, and Silk. 5. Analysis of Weighting in Silk Fabrics.

APPENDIX I.

Microscopic Analysis of Fabrics 269

APPENDIX II.

Machine for Determining Strength of Fibres 272

APPENDIX III.

Bibliography of the Textile Fibres 275

Index 279

THE TEXTILE FIBRES.

Chapter I. Classification Of The Textile Fibres

1. Fibres Chiefly Used for Textiles. — In order to be serviceable in a textile fabric, a fibre must possess sufficient length to be woven and a physical structure which will permit of several fibres being spun together, thereby yielding a continuous thread of considerable tensile strength and pliability. Although there are several fibres, such as spun glass, asbestos, various grasses, etc., which are used for the manufacture of textiles in peculiar and rare instances, yet the fibres which are employed to the greatest extent and which exhibit the most satisfactory qualities are wool, silk, cotton, and finen. All of these possess an organized structure, and are the products of a natural growth in life processes.

According to Georgevics, all textile fibres may be divided into four distinct classes; and though the same general arrangement is here preserved, the order has been somewhat changed so as to bring the most prominent ones first: (i) Animal fibres; (2) Vegetable fibres; (3) Mineral fibres; (4) Artificial fibres.

2. Animal and Vegetable Fibres. ^According to their origin, we may divide the principal fibres into two general classes, those derived from animal and those derived from vegetable Hfe. The former includes wool and silk, and the latter cotton and linen. Animal fibres are essentially nitrogenous substances (protein matter), and in some cases contain sulphur. They may be solid filaments formed from a liquid secretion of certain caterpillars, spiders, or molluscs. Alkalies readily attack the animal fibres, causing them to be dissolved, but they withstand the action of mineral acids to a considerable degree. Contrary to the vegetable fibres, they are readily injured if exposed to elevated temperatures. Vegetable fibres consist of plant-cells, usually rather simple in structure and forming an integral part of the plant itself. They are capable of withstanding rather high temperatures, and are not weakened or disintegrated by the action of dilute alkalies. They consist essentially of cellulose, which may be in a very pure form, or be mixed with its various alteration products. In some cases the fibre consists of some cellulose derivative obtained by chemical means, such, for instance, as mercerized cotton. Concentrated alkalies produce alteration products with the vegetable fibres. Free sulphuric or hydrochloric acid, even if only moderately strong, will quickly attack the fibre, disintegrating its organic structure and forming hydrolyzed products. Nitric acid, on the other hand, forms nitrocelluloses and various oxidation derivatives.

3. Mineral and Artificial Fibres. — ^These two classes of fibres are of rare occurrence in the textile industry when compared with the extensive use of the preceding fibres. They find a limited use, however, for certain purposes, and deserve to be considered in a systematic study of the subject. The principal, and strictly speaking the only, mineral fibre is asbestos, which occurs in nature as the mineral of that name. It is a fibrous silicate of magnesium and calcium, though often containing iron and aluminium in its composition, especially in the dark-colored varieties. This mineral, though in the form of a hard rock, can be easily separated into slender white fibres, sometimes inclining towards a greenish color. The fibres of some varieties (Canadian) are curly, and afford the best material for spinning. In general, however, the fibres of asbestos are straight and glassy in structure, and are difficult to spin into a coherent thread. In order to enhance its spinning qualities it is mixed with a little cotton, the latter fibre being subsequently destroyed by heating the woven

CLASSIFICATION OF THE TEXTILE FIBRES. 3

fabric to incandescence. At the present time quite a variety of fabrics are manufactured from asbestos fibre, and the high quahty of many articles appearing on the market shows that the art of manipulating this substance has reached a high degree of perfection. On account of its incombustible nature, and as it is a very poor conductor of heat, it is made into fabrics where these qualities are especially desired. Thus it is frequently manufactured into gloves and aprons, packing for steam- cylinders, theatrical curtains and scenery, lamp-Avicks, etc. The latter use of asbestos was known to the ancients, who employed it for the wicks of the perpetual lamps in their temples. It is from this fact, indeed, that it received its name, the word "asbestos" meaning "unconsumed." It was also employed for napkins on account of its being readily cleansed, it only being necessary to heat the fabric in a flame to make it clean again. Asbestos, in general, is not dyed, and does not undergo any chemical processes or modes of treatment. When it is desirable to dye it the various substantive dyes may be used with good effect, or the color may be applied by mordanting with albumen.

The artificial fibres may be divided into two groups: (a) those of mineral origin and (b) those of animal or vegetable origin. In the first division may be classed such fibres as spun glass, metallic threads, and slag wool; in the second division may be put the various artificial silks, such as lustra-cellulose and gelatin silk.

Fibres of spun glass are prepared by drawing out molten glass in the form of very fine threads ; colored glasses may be used to give rise to variously colored threads. Owing to its brittle nature and lack of elasticity, spun glass receives a very limited application, it being made into various ornamental objects, and sometimes into cravats. A variety of spun glass known as glass wool is used to some extent in the chemical laboratory as a filtering medium for liquids which would destroy ordinary filter-paper. Glass wool is curly, this property being given to it by drawing out the glass thread from two pieces of -glass of different degrees of hardness; and by unequal contraction on cooling, this double thread curls up.

Various metals are at times drawn out into threads for use in decorative fabrics. Gold, silver, copper, and various alloys are used for this purpose. At the present time metallic threads are largely imitated by coating linen yarns w^ith a thin film of gold or silver.

Slag wool is prepared by blowing steam through molten slag;, it can scarcely be called a textile fibre, but it is used in some degree as a packing material.

Artificial silks are made either from cellulose derivatives or gelatin by forcing solutions of these through fine capillary tubes and coagulating the resulting threads and subsequently subjecting them to various processes of chemical treatment. As these belong more strictly to the class of true textile fibres, they will be given a more extensive consideration, in a further section, as being derivatives of cellulose.

Chapter II. Wool And Hair Fibres

I. The woolly, hair-like covering of the sheep forms the most important and the most typical of the textile fibres which are obtained from the skin tissues of different beasts. The hairy coverings of a large number of animals are employed to a greater or lesser extent as raw materials for the manufacture of different textile products, but those of the various species of sheep make up the great bulk of the fibres which possess any considerable technical importance. Hairs, derived from whatever species of animals, have very much in common as to their general physical and chemical properties; they are also similar with respect to their physiological origin and growth. The hairs, however, of different animals, vary much in the detail of their special characteristics, and also with regard to their adaptability for use in the textile industry; and the wool of the sheep appears to exhibit in the highest degree those specific properties which make the most suitable textile fibre. These properties may be enumerated as being: (a) Sufficient length, strength, and elasticity, together with certain surface cohesion, to enable several fibres to be twisted or spun together so as to form a coherent and continuous thread or yam; (b) the power of absorbing coloring- matters from solution and becoming dyed thereby, and also the property of becoming decolorized or bleached when treated with suitable chemical agents; (c) in addition to these quahties, which they have in common with almost any textile fibre, wool fibres also possess the quahty of becoming felted or matted together, due to the pecuHar physical character of their surfaces. This property is a most valuable one, as it adapts wool to a large number of uses to which other fibres are unsuitable.

Silk is also a member of the general group of animal fibres, and though it possesses certain general chemical characteristics in common with wool and hair, yet it has an entirely different physiological origin, being a filament of animal tissue excreted by a certain species of caterpillar, and hence is totally different ■from wool in its physical properties. Wool may be specifically designated as a variety of hair growing on certain species of mammalia, such as sheep, goats, etc. The unmodified term " wool " has special reference to the product obtained from the different varieties of sheep. Cashmere, mohair, and alpaca are the products obtained from the thibet, angora, and llama goats, respectively. Fur is also a modified form of hair, but differs from wool in many of its physical properties, and is not adapted for use in the manufacture of spun textiles. It is, however, largely employed for the making of hat felts.

The wool-bearing animals all belong to the order Ruminantia, which includes those animals that chew their cud or ruminate. The principal members of this order are sheep, goats, and camels. The sheep belongs to the class Ovida, and occurs in a number of species which vary considerably in form and geographical distribution, as well as in the character of the wool it produces. Broadly considered, naturalists divide the sheep into three different classes:

{a) Ovis arles, commonly known as the domestic sheep, and cultivated more or less in every country in the world.

(b) Ovis musmon, occurring native in the European and African countries bordering on the Mediterranean Sea.

(c) Ovis ammon, which includes the wild or mountain sheep (argali) to be found in Asia and America. The big-horn sheep of the Rocky Mountains belongs to this class.*

* A more detailed classification than the above is given by Archer, who divides the sheep into thirty-two varieties:

1. Spanish, or merino sheep (Ovis hispaniam).

2. Common sheep (Ovis rusiicus). ;^. ^Cretan sheep {Ovis strepsiceros).

The domestic sheep is the most important of these classes. It can hardly be said to be indigenous to any one country, for it appears to have been cultivated by the earliest peoples in history, and it has spread over the entire face of the globe with the gradual extension of civilization itself. Different conditions of climate and soil, of pasturage and cultivation, appear to exert a considerable influence on the variety of the sheep and on the character of the w^ool it eventually produces. Variations are also produced

4. Crimean sheep {Ovis longicandatus) .

5. Hooniah, or black-faced sheep of Thibet.

6. Cago, or tame sheep of Cabul {Ovis cagia).

7. Nepal sheep {Ovis selingia). 8 Curumbar, or Mysore sheep. 9. Garar, or Indian sheep.

10. Dukhun, or Deccan sheep.

11. Morvant de la chine, or Chinese sheep.

12. Shaymbliar, or Mysore sheep.

13. Broad-tailed sheep {Ovis laticandatus) .

14. Many-horned sheep {Ovis poly ceratus).

16. Tartary sheep.

17. Javanese sheep.

18. Barwall sheep {Ovis Barnal).

19. Short-tailed sheep of northern Russia.

20. Smooth-haired sheep {Ovis Ethiopia).

21. African sheep {Ovis Grienensis).

22. Guinea sheep {Ovis atnmon Guinensis).

23. Zeylan sheep.

24. Fezzan sheep.

25. Congo sheep {Ovis aries congensis).

26. Angola sheep {Ovis aries angolensis).

27. Yenu, or goitred sheep {Ovis aries steatiniora).

28. Madagascar sheep.

29. Bearded sheep of west Africa.

30. Morocco sheep {Ovis aries muncBdcB).

31. West Indian sheep of Jamaica.

32. Brazilian sheep.

These represent the naturally occurring classes of sheep in the different countries; of course, a large number have been emigrated and domesticated in other countries than those in which they had their origin, which has given rise to several sub-varieties. Then, too, new varieties have been formed by cross-breeding and intermixing, which has brought about a considerable variation in the type. The latter is also influenced very largely by climatic conditions, geographical environment, and character of pasturage.

by cross-breeding and intermixing, and the nature of the fibre has been much altered and improved by careful selection in breeding and genealogical development.

Sheep in their natural condition produce two kinds of hair: the one giving a long, stiff fibre, which we will call " beard- hair "; and the other a shorter, softer, and more curly fibre, which we will designate as " wool-hair," or true wool. By domestication and proper cultivation the sheep can be made to produce the latter kind of hair almost exclusively, with but little or none of the hairy fibre. Herein the sheep differs essentially from the goat, as the latter will always produce both kinds of fibre, though the fineness and quality of its hair may be much improved by proper cultivation. In addition to the above-mentioned varieties of hair, most sheep grow more or less of short, stiff hairs, or undergrowth; these have no value as textile fibres. It must be mentioned, however, that the exact character of the wool on the individual sheep varies considerably with its position in the fleece; on the extremities of the animal the wool becomes more hairy in nature, and near the feet the short undergrowth of stiff hair is alone to be found. The texture, length, and softness of the fibre also differ considerably in different portions of the fleece. Hence it becomes necessary, in order to obtain a homogeneous mixture of fibres with properties as constant as possible, to sort out the fibres of the fleece into different portions, which are put together into different grades of wool stock. This operation is termed wool-sorting and grading, and is an important step in the manufacture of wool. Different varieties of wool may require different systems and degrees of sorting, but in general the fleece is roughly divided into nine sections, given as follows:

(i) The shoulders and sides of the fleece give the finest and most even staples of fibre.

(2) The lower part of the back yields a fibre of fairly good staple.

(3) The loin and back give a shorter staple, and the fibre is not as strong.

(4) The upper part of the legs give a staple of moderate length. The fibre on this part is frequently in the form of loose,

^VOOL ^ND HAIR FIBRES. 9

open locks and acquires a large amount of burrs by brushing against the spinose fruit of the plant; the presence of these burrs considerably lessens the commercial value of the wool. South American wool is especially liable to be heavily charged with burrs.

(5) The upper part of the neck gives a rather irregular staple which is also very frequently filled with burrs.

(6) The centre of the back gives a fine delicate staple similar to that from the loins.

(7) The belly, together with the wool from the fore and hind legs yields a poor staple and a weak fibre.

(8) The tail gives a short, coarse, and lustrous fibre, frequently containing a considerable amount of kemps.

(9) The head, chest, and shins give a short, stiff, and straight fibre, opaque and dead white in color.

The merino sheep, which yields what is considered to be the finest quality of wool, appears to have originated in Spain, and at one time was extensively cultivated by the Moors. The exportation of merino sheep from Spain was long guarded against with great care, no one being allowed to take a live merino sheep out of the kingdom of Spain under penalty of death. Later, however, this sheep was brought into various countries, being crossed with the different local breeds with very beneficial results. A German derivative of the Spanish merino known as the Saxony Electoral merino, gives perhaps the highest grade of fibre known in Europe. Australian sheep are mostly derived from merino and other high- class stock and yield a wool of the very highest quality. The merino has been cultivated and crossed with other breeds throughout the various parts of the United States, and the latter country is gradually becoming a large producer of middle grade wool.

2. Physiology and Structure of Wool. — Wool, in common with all kinds of hair, is a growth originating in the skin or cuticle of the vertebrate animals, and is similar in its origin and general composition to the various other skin tissues to be found in animals, such as horn, nails, feathers, etc. Wool is an organized structure growing from a root situated in the dermis or middle

THE TEXTILE FIBRES.

layer of the skin; its ultimate physical elements being several series of animal cells of different forms and properties. Herein it differs essentially from silk, which is not composed of cells, but is a continuous and homogeneous tissue. The root of the wool fibre is termed the hair folHcle (Fig. i) ; it is a gland which secretes

-pj:

Fig. I. — Section of Hair Follicle.

C, cuticle of skin; R, reta mucosum; PL, papillary layer; S, sebaceous glands; P, papilla; B, bulb of hair; H, hair; F, fibrous tissue; SH, transparent sheath.

a lymph-like hquid, from which the hair is gradually developed by the process of growth. The hair folHcle also secretes an oil, which is supplied to the fibre during its growth, and serves the purpose of lubricating its several parts, giving it pliability and elasticity. In conjunction with the hair folhcle there also occur in the skin numerous sebaceous glands which secrete a fatty or waxy substance, commonly known as wool-fat. This substance

IVOGL AND HAIR FIBRES.

gradually exudes from the glands and coats the surface of the wool in rather considerable amount (Fig. 2). It affords a protective coating to the fibre which serves to preserve the latter from mechanical injury during its growth, and also prevents the several fibres from becoming matted and felted together. In the preparation of wool for manufacture, this fatty covering has to be removed, the operation constituting the ordinary process of wool scouring. The oil, on the other hand, which is contained in the substance of the fibre itself, and is a true constituent of its sub-

FiG. 2. — ^Wool Fibre in the Natural Grease (X350). The markings of the scales are scarcely apparent owing to the interstices being filled with greasy matter.

stance, should not be removed, as its removal causes the fibre to lose much of its elasticity and resiliency. This oil amounts to about one per cent, of the total weight of the fibre, whereas the external fatty matter amounts on an average to about 30 per cent. Morphologically considered, the wool fibre consists of three distinct portions: (a) A cellular marrow, or medulla, which frequently contains more or less pigment matter to which the wool owes its color; (6) A layer of cellular fibrous substance or cortical tissue which gives the fibre its chief strength and elasticity; (c) An outer layer or epidermis of horn tissue, consisting of flattened cells, or scales, the ends of which generally overlap each other, and project outwards, causing the edge of the fibre to present a serrated appearance (Fig. 3). This scaly covering

THE TEXTILE FIBRES.

gives the fibre its quality of rigidity and resistance to crushing strain; it also causes the fibres to felt together on rubbing against one another by the interlocking of the projecting edges of the scales (Fig. 4).

Any one of these three physical constituents may at times be lacking in a fibre. When the epidermal scales are absent, they have simply been rubbed off by friction; this condition is fre-

FiG. 3. Fig. 4.

Fig. 3. — Sections of Wool or Hair Fibre. a, cross-section of fibre; h, longitudinal section of fibre; A, epidermal layer of scales; B, cortical layer of fibrous cells; C, medullary layer of round cells. Fig. 4. — Diagram Showing Felting Action of Wool.

quently to be found at the ends of long beard-hairs. The cortical layer of fibrous tissue is frequently but slightly developed, especially in cases where the medulla is large : in some instances, indeed (as in the hair of the doe), the cortical layer appears to be totally absent in the broadest parts of the fibre. The medulla is very frequently absent, or, at least, shows no difference in structure from the cells of the surrounding cortical layer; this occurs more especially in the wool- hairs, but is also to be found in beard-hairs. On the other hand, the medulla is more largely developed than the cortical layer, and becomes the principal part of the fibre, as in the beard-hairs of the doe.

The microscopic appearance of wool is sufficiently characteristic to distinguish it from all other fibres. Under even moderately low power of magnification the scales on the surface of the fibre can be readily discerned, while neither silk nor the vegetable fibres present this appearance (Fig. 5). The scales

Fig. 5. — \'arious Fibres. (Bowman.) A, Chinese wool; B, merino wool; C, cotton; D, silk; E, mohair.

are more or less translucent in appearance, and permit of the under cortical layer being seen through them. The exact nature and structure and arrangement of the scales differ considerably with different varieties of wool. In fine merino wools, for instance, the individual scales are in the form of cylindrical cusps, one somewhat overlapping the other; that is to say, a single scale completely surrounds the entire fibre (Fig. 6). In some varieties of wool, on the other hand, two or more scales occur in the circumference of the fibre. In some cases the edges of the scales are smooth and straight (Fig. 7), and this appears to be especially characteristic of fine qualities of wool; the coarser species, on the other hand, possess scales having serrated wavy

THE TEXTILE FIBRES.

edges. Usually such scales are much broader than they are long and are very thin (Fig. 8). The length of the free or projecting

Fig. 6. — Typical Wool Fibres (X500).

From a camera lucida micrograph, showing the irregular surface scales and the faint striations of the underlying fibrous layer of cortical tissue; the presence of the medullary cells is also plainly visible in one fibre.

Fig. 7.— Wool Fibre (X350).

With smooth, straight scales of a non-felting type.

edge of the scale is also a very variable factor; in some wools the scale is free frorg the body of the fibre for about one-third of the

WOOL /iND H^IR FIBRES. 15

length of the former, and in consequence the scale protrudes to a considerable extent; such wool would be eminently suitable for the preparation of material which requires to be much felted (Fig. 9). In other wools, the free edge of the scale amounts to almost nothing, and the separate members fit down on one another closely, and are arranged like a series of plates. Wools of this class are more hair-like in texture, being stiffer and straighter.

Fig. 8. Fig. 9.

Fig. 8. — American Merino Wool. (Bowman.)

Fig. 9. — Australian Botany Wool. (Bowman.)

In fibres A and B irregularities in diameter may be noticed; but in fibres C and D

the diameter is very uniform.

and not capable of being readily felted (Fig. 10). The wool-hairs (the long, stiff fibres which have already been mentioned as occurring to a greater or lesser degree in nearly all wools, also known as beard-hairs) usually possess this structure. The felting quality of wool is much increased by treatment with acid or alkaline solutions, or even boiling water, the effect being to open up the scales to a greater extent, so that they present a much larger free margin and consequently interlock more readily and firmly. Woolen yams, and woven materials made from such yarns, felt much more easily than worsted yarns, due to the fact that the fibres of the former lie in every direction and the interlocking of the scales takes place more easily.

In some varieties of wool fibre the scales have no free edge at all, but the sides fit tightly together with apparently no overlapi6

THE TEXTILE FIBRES.

ping; in such fibres the surfaces of the scales are also more or less concave (Fig. ii). This structure only occurs with thick, coarse varieties of wool. Frequently at the ends of the wool fibre, where the natural point is still preserved (as in the case of

Fig. 10. — ^Wool Fibre with Plate-like Scales. (Hohnel.)

A, portion of fibre with isolated medullary cells at i, and smooth scales e fitting

together like plates; B, portion of fibre showing medullary cylinder at m.

lamb's wool from fleeces which have not been previously sheared), the scales are more or less rubbed off and the under cortical layer becomes exposed (Fig. 12); this appearance is quite characteristic of certain wools. In diseased fibres the epidermal scales may also be lacking in places, causing such fibres to be very weak at these points (Fig. 13).

In most varieties of wools the scales of the epidermis may be readily observed even under rather low powers of magnification, while under high powers the individual scales may be seen overlapping one another like shingles on a roof, and showing pointed, fVOOL /iND H/ilR FIBRES.

Fig. II. Fig. 12.

Fig. II. — -Wool Fibre with Concave Scales. (Hohnel.) m, medullary cylinder consisting of several rows of cells; e, concave scales arranged in a plate-like manner.

Fig. 12. — Showing Wool Fibre with Scales Rubbed Off. (Hohnel.) e, residue of epidermis; notice the coarse striations of the cortical layer underneath the epidermis.