Super Suber

A trunk of 50-year old cork oak,
Quercus suber, at The Huntington

Most trees make cork; it’s a dead tissue in the bark, a tissue called phellem in Greek and suber in Latin.  Botanists still use the words phellem and suber to describe barks, but in English we just say cork, a term that likely derives from quercus, which is the Latin word for oak trees.  Of course the reason for this connection is that Mediterranean peoples knew and valued the Cork Oak for its super thick bark.  Cork Oak was familiar to European botanists, and it was no surprise that in 1753 Linnaeus accepted the name Quercus suber (from the Latin quercus for oak, and suber for cork), which became its scientific name.

Large groves of Cork Oak trees are cultivated for bark harvest (mostly in Spain and Portugal).  Following a very skilled and patient process, growers peel thick, even sheets of corky bark on a sustainable schedule.  It’s tough, lightweight, and water-resilient, with many historical uses.  

The floor of the main Library exhibit hall, installed in 1919, is made of cork.  Some of the aristocrats portrayed in Huntington grand manor portraits might have kempt cork-soled chopines to wear with their full-length gowns. Before plastics, cork was a standard substance for fishing line floats and bobbers.  Beginning with Digby’s introduction of the modern wine bottle around 1632, cork was adopted as the principal material used to stopper wine bottles, and still remains the source for most champagne stoppers.

Illustration from Hooke’s Micrographia

As cork becomes less necessary in construction and manufacturing, it may drift from everyday experience.  But cork will always be remembered in the world of biology – not simply as a handsome substance that protects trees.  A visit to Beautiful Science allows visitors to examine a reconstruction of the microscope Robert Hooke used to examine natural materials, work that led to his Micrographia, one of the first books on microscopy.  Studying thin slices of cork, Hooke described its structure as that of hollow vesicles he called cells, going to the extent of calculating there could be twelve hundred million such cells in a cubic inch of cork.*  It seems clear from the text that he thought these were tiny bladders or particulates that somehow produced the waterproof sponginess special to cork. Minimally, it’s clear that neither Hooke nor anyone else at the time understood the significance of his observations on cork cells. Regardless, Hooke’s discovery – and the word “cell” – remain at the foundation of all modern life sciences.

*  More recent studies suggest there are about 300 million cells in a single wine bottle cork. 

Useful References:

Gibson, L. J., K. E. Easterling and M. F. Ashby, 1981. “The Structure and Mechanics of Cork”. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 377 (1769): 99-117 (The paper states there are 20,000 cells in a cubic mm of cork)

George M. Taber, 2007.  To Cork or Not to Cork: Tradition, Romance, Science, and the Battle for the Wine Bottle, Scribner, NY

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