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Cork, or phellem, is a protective plant tissue produced by the cork cambium. Mature cork consists largely of dead biological cells whose cell walls contain suberin, a material that limits passage of water. Cork forms part of the outer protective covering of mature plant stems and the root; it is not a name for every component of bark.

Commercial cork comes from the especially thick outer bark of Quercus suber. Comparing actively forming cork with other plant tissues connects its useful barrier properties to gene expression involved in suberin production. Such comparisons have identified candidate pathways in cork differentiation rather than treating the material simply as inert packing.^[ref]

Marçal Soler is a plant researcher credited as first author of a 2007 study of suberin synthesis and cork differentiation in Quercus suber. The paper identifies an affiliation with the cork laboratory in the Department of Biology at the University of Girona.

The team enriched for RNA associated with cork formation and used a microarray to compare expression in cork and xylem. The comparison identified candidate genes for the protective suberin barrier. Differential gene expression narrows a list of candidates; it does not alone prove that every enriched gene catalyses a particular biosynthetic step. This is a concrete example of using genomics to turn a conspicuous plant material into testable molecular questions.^[ref]

Quercus suber, the cork oak, is an evergreen tree native to the western Mediterranean region. Its thick bark supplies commercial cork, which can be harvested repeatedly when the living layers needed for regeneration are preserved.^[ref]

Cork consists of protective tissue whose cell walls contain suberin, a material that limits water loss. This makes Quercus suber a useful system for investigating how a plant builds an external barrier. Comparing gene expression in developing cork with expression in xylem identified candidate genes associated with suberin synthesis and tissue differentiation.^[ref] The commercial material is therefore also a tractable product of a specific developmental programme.

Robert Hooke used microscopy to connect the visible properties of material with structures too small to inspect unaided. In Micrographia by Robert Hooke, his examination of cork revealed many tiny compartments, which he called cells. He related this architecture to the material's lightness, resistance to absorbing water and recovery after compression. The account records the specimen preparation, illumination and observed structure, making the instrument and viewing conditions part of the evidence for the interpretation of plant tissue.^[ref]