Fiber Morphology Definitions used in the Fiber Reference Image Library

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Plant stem fibers

Lumen types

In recording the lumen characteristics of each fiber as it is examined under the microscope the following categories are used. 1. Not apparent. Lumen may not be apparent when using some techniques of microscopy. 2. Wide. The lumen width is wide compared to the width of the fiber 3. Narrow. The lumen is narrow compared to the width of the fiber. 4. Variable. The lumen width is variable along the length of the fiber.

Lumen filling

In some cases, the lumen appears infilled with material of different color and character than the remainder of the phloem fiber. In recording whether the apparent lumen contains a filling or not, the following categories are used. 1. not apparent. No filling within the lumen can be seen. 2. segmented filling 3. solidly filled lumen. 4. square shaped filling materials 5. irregular filling materials


The fiber shows evidence of swelling if the dislocations protrude. In addition, the fibrils are evident.


Fibers display bulging along their length at regular or irregular intervals due to degradation or growth conditions. A bulge is a one or two sided protrusion from the fiber. The bulging is not the same as the protrusion associated with a dislocation. It is distinguished from swelling in that no fibrils are evident as distinct entities in the bulge.


A fiber is characterized as showing "fibrillation" if the fibrils are apparent within the fiber structure. The fibrils may or may not show separation from each other within the fiber structure.

Fiber size categories

Fiber sizes are visually estimated at nominal 400 X magnification and categorized as: 1. wide, 2. medium, 3. thin, 4. variable.


The dislocations observed in the fibers are categorized according to the following types. 0. None 1. Few 2. Moderate 3. Many

Distinction is made between a dislocation and some other type of cross marking. Dislocations form while the fiber is growing, cross markings can result from treatment during growth or processing. Cross markings are irregular in placement and do not necessarily compose a feature which extends across the width of the fiber.


Disruptions in the fiber surfaces are noted when the surfaces are notably irregular and uneven. The disruptions are not localized as are dislocations.

Transverse markings, cross markings

A fiber may have marks running across its width which are distinct from cracks, because there is no fissure apparent. The transverse marking also is distinct from the dislocation because the marking is a surface-only phenomenon which does not result from folding of the fibrils in growth.

Longitudinal markings

Longitudinal markings are striations which run parallel with the length of the fiber. They are not evidence of fibrillation. In fact, fibrillation or swelling which shows evidence of fibrils will be revealed in a spiralling fibrillar structure characteristic of the fibrillar arrangement within bast fibers.


Fibers exhibit kinks in their structure when, at a point of a dislocation, the fiber takes a true bend in the direction of its growth. The kink is a fairly abrupt bend along the fiber length. In fiber bundles, the kink is exhibited by all fibers within the bundle at the same location.


A fiber which exhibits a crack shows a marked fissure in the fiber. It can be distinguished from a transverse marking because the fiber is separated at the point of the fissure.


A fissure is a crack within the fiber which extends across the fiber for at least half of the width of the fiber.

Crystals, mineral inclusions

Plant materials can contain crystal inclusions (the literature cites silica and calcium oxalate crystal phytoliths in dietary plants). These are noted in the materials surrounding the fibers themselves, and often form within the parenchyma cells. These are more apparent when observed under polarized light. Types of crystals include rhombic, clusters, clusters in chains, cubic, acicular. The crystals observed in the fibers are categorized according to the following types. 0. None 1. Few 2. Moderate 3. Many


Plant stem fibers which are still in bundle form may show evidence of associated tissues. The cambium surrounding fiber bundles is characteristically amorphous in structure and acts as a "glue" to hold the fibers together.

Parenchyma Cells

Plant stem fibers which are still in bundle form may show evidence of associated plant cell structures. Parenchyma cells have a characteristic almost spherical shape. The presence of these cells indicate that the fibers (schlerenchyma cells) were not very well separated from other plant structures in processing.

Animal Fibers


The outer cuticule of animal hair fibers creates patterns of overlapping scale structures, which are often used to aid in fiber identification. In some cases, a special sample preparation such as an air mount or a cast, is employed to provide better visualization of these surface features.


Medullary cells are inner structures visible in some hair fibers when examined by transmission optical microscopy. Further distinction is often made by microscopists based on shape and continuity of the medullary cells.

Manufactured Fibers


Some synthetic fibers have delustrant added to spin solution, consequently the particles of delustrant are visible in optical microscopy.

Surface morphology

Many manufactured fibers are extruded through spinnerettes which can influence the consequent cross sectional shape. In addition, some fiber spin solutions, upon extrusion, collapse or change such that the cross sectional shape is changed. Thus some manufactured fibers are smooth on their surface while others display longitudinal striations.

Sign of elongation

Examination of man-made fibers under polarized light and employing an additional compensator in the optical pathway provides evidence for the difference in Refractive Indices (RI) of man-made fibers along their length and across their width. A fiber with a RI that is higher longitudinally than across its width is labelled positive.