GENKKAL MICKOSCOI'Y 



phology and examination with special meth- 

 ods such as micro-chemical reactions and 

 examination in polarized light. The normal 

 bright field methods can be applied very 

 suitably. Phase contrast microscopy with 

 special mounting methods is very important 

 for examining micro structures and for trac- 

 ing mercerizing. Dark field microscopy can 

 also be used for examining surface structures, 

 and the same applies to incident light micros- 

 copy. 



The fiber is a single cell and looks like an 

 irregularly twisted, collapsed tube with a 

 central canal or lumen. No lumen can be 

 seen at the top of the unbroken fibers. In its 

 undamaged state the basal part of the fiber 

 shows a membrane (part of the fiber that was 

 underneath the seedcoat). The twists often 

 change from Z to S spirals. There are three 

 cross-sectional shapes — round, elliptic and 

 hnear. 



Dead cotton fibers are often U-shaped in 

 cross section, no lumen being visible. 



The cross section varies very greatly from 

 fiber to fiber. In this cross section the pri- 

 mary wall, the secondary wall, and the lumen 

 can be distinguished. 



The outside of the fiber is covered with a 

 cuticula consisting of wax and pectin. The 

 primary wall consists of fibrils oriented at 

 random. The secondary wall consists of vari- 

 ous layers deposited within each other, which 

 are easiest to see in swollen material. The 

 secondary wall also consists of fibrils oriented 

 spirally. 



The usual swelling medium is copper oxide 

 ammonia. This swells the fiber irregularly. 

 At certain intervals there are zones which do 

 not swell. Often a spiral structure is also left, 

 probably originating from protoplasm resi- 

 dues. In iodo-sulfuric acid the fibers swell 

 and turn blue; protoplasm residues turn yel- 

 low. Ruthenium red, together with copper 

 oxide ammonia, has the result that the cu- 

 ticula, the wall of the lumen and the proto- 

 plasm residues turn red. 



Zinc chloroiodide stains the fiber reddish 

 violet. Mercerized cotton and bleached cot- 



ton color with this reagent more strongly 

 than raw cotton. With copper oxide ammonia 

 mercerized cotton forms no globules. 



The fibrils lie next to one another in each 

 layer of the secondary wall and are oriented 

 spirally relatively to the long axis. The direc- 

 tion of the spiral is often reversed and coin- 

 cides with a reversal in the external twisting. 

 The dimensions of the fibrils have been de- 

 termined with an electron microscope. 



Damage to Cotton Fibers. Mechanical 

 Damage. The forms of mechanical damage 

 that may occur are irregular cross fracture, 

 bruises and places where the fiber has been 

 unevenly torn off. 



Chemical Damage. This results in gradual 

 decomposition of the cuticula, shown by an 

 emphasizing of the spirals. In the case of 

 chemical attack by acids, the spirals can be 

 seen all over the fiber. Photo-chemical de- 

 composition is usually more highly localized. 



Biological Attack. Morphologically this 

 closely resembles chemical damage. As a rule, 

 however, the hyphae of the fungi or bacteria 

 colonies are demonstrable. 



Flax (Fig. 2a). Flax consists of cylindrical 

 cells which are usually smooth except at the 

 location of the usually X-shaped internode. 

 The cross section is round to polygonal; the 

 cell wall is thick. There is a narrow, well-de- 

 fined lumen. At the end of the cell the lumen 

 is lacking. The lumen has an independent 

 existence. In Cuoxam it forms a small tube 

 that remains even after the fiber is com- 

 pletely dissolved. Zinc chloroiodide colors 

 unbleached flax pale violet, while bleached 

 flax colors dark violet. In Neocarmine W 

 flax turns blue. 



Hemp (Fig. 2b). Hemp is often difficult 

 to distinguish from flax. The differences are: 

 (1) hemp cells are blunt-ended, forking later- 

 ally; (2) in iodine-sulfuric acid hemp shows 

 cross striation and a l)lue-green color (flax: 

 blue) ; (3) hemp fibers are not as transparent 

 as flax fibers; (4) the cross section is different; 

 (5) the parenchyma tissue often attached to 

 the fiber contains calcium oxalate crystals. 



With iodo-sulfuric acid a blue-green color 



356 



