Lumen
Also searched as: fibre lumen, central canal, cell cavity, lumen collapse
The central cavity inside a plant fiber cell, left as the cell wall thickens; its size and collapse shape cotton's twisted form and relate directly to fiber maturity.
In detail
Plant fibers are single cells, or bundles of cells, whose walls thicken from the outside inward. A cotton fiber begins as a tubular seed hair with a wide central cavity, and as the secondary wall deposits cellulose, that cavity narrows. When the boll opens and the fiber dries, the cell collapses into a flattened, bean-shaped cross-section with a small residual lumen, and this collapse contributes to the characteristic twists along the fiber. Bast fibers such as flax also have a central lumen, surrounded by thick secondary walls built in layers. Because the lumen is an internal space, it can hold water and treatment chemicals.
The science and numbers
In a growing cotton fiber the lumen occupies roughly a third of the cross-section, and after drying and collapse it shrinks to about 5% or less. Maturity is expressed through measurements on cross-sections: circularity C equals 4 pi A divided by the square of the perimeter, and the degree of thickening Tr equals 2 pi T divided by the perimeter, where A is the wall area and T the wall thickness; both range from 0 to 1. In flax, each elementary fiber has a lumen enclosed by a primary wall and a secondary wall in three sublayers, S1 next to the primary wall, then S2, and S3 lining the lumen. In the living plant the lumen carries water and nutrients by capillary action.
A practical example
Students cut cross-sections of immature and mature cotton fibers and view them under a microscope. The immature fibers show thin walls around a large, flattened lumen and look ribbon-like, while the mature fibers have thick walls and only a small central cavity. The class then relates what they see to the circularity and wall-thickening ratios that laboratories use to express cotton maturity numerically.
What to distinguish
A plant fiber's lumen is a natural cell cavity, not the engineered hollow core of some manufactured fibers. Lumen size alone does not measure maturity, which depends on wall thickness relative to the fiber's perimeter. Animal fibers do not have a lumen: the core some of them contain is the medulla, a different structure made of cells and air spaces.
Origins and history
Lumen is Latin for light, and by extension an opening, and anatomists use it for the cavity of any tube, from blood vessels to plant cells. In fiber science it names the space left inside a cell once its wall has formed. Cotton breeders and testers have long linked lumen and wall development to maturity, and cross-sectional image analysis in the late twentieth century was used to develop reference standards for cotton maturity measurement.
Related terms
Sources & further reading
- Journal of Cotton Science (National Cotton Council): Development of new reference standards for cotton fiber maturity
- PMC: Cotton fiber as a model for understanding shifts in cell development under domestication
- ScienceDirect Topics: Cotton fibre, an overview
- Cellulose (Springer): Extraction of cellulose fibers from flax and hemp, a review
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.