Plant of the month (©Pierre Laszlo, all rights reserved)
The mulberry tree, Broussonettia papyrifera (Moraceae)
Paper is named after papyrus, a reed that ancient Egyptians turned into a writing support. Independently, the Chinese resorted to other plants for their ancient papermaking. French archeologists found an extremely ancient piece of paper in a tomb in Mongolia, to this day the oldest such find. The analysis dates it to the end of the 1st century BC — it was carried out by Véronique Rouchon, a former student of mine, now a professor at Muséum national d’histoire naturelle in Paris — and it showed that it was made primarily from hemp fibers and, secondarily, linen fibers.
The main raw material for papermaking in China, for many centuries, was, however, the mulberry tree. This plant is a close relative to another species of mulberry tree used for raising silkworms — indeed their larvae can also feed on its leaves. Such use originated in China during the Han dynasties, around 100 AD. The plant indeed had Chinese origins.
Due to papermaking, it spread to Korea and Japan, Southeast Asia and India. Other fiber uses, to tapa cloth, brought it to the South Seas (Fiji, Tonga, Samoa and Tahiti). Arab traders supplied it to Europeans. After the sevententh century, the paper mulberry — as the tree became known — spread to most of the rest of the world.
Paper manufacture, threatened with decline in our age of electronics and the Internet, in any case no longer demands cultivation of mulberry trees. Prior to the Industrial Revolution, rags and other useless textiles started serving as substitute material. In the aftermath, cotton and wood from species such as pinetrees became the main raw materials for paper production.
But mulberry paper is still with us. It occupies a niche of high quality stationary. Asians have a predilection for this handsome paper. I can offer no better instance than the Itoya store, in the Ginza shopping area of Tokyo. Ever since I discovered this paper-lover paradise in the summer of 1979, it has marked every single visit of mine to Tokyo — the latest in March 2015. Mulberry-paper-based stationery at Itoya is gorgeous, their Thai imports in particular.
How does papermaking proceed from the paper mulberry? The inner bark, known as the phloem, very white indeed, is boiled with chemicals such as baking soda in order to dissociate the fibers. They are then beaten into a pulp, afterwards diluted into a fiber suspension. The aqueous heterogeneous mix is poured upon a screen, to create a mat of interwoven fibers, i.e., a sheet of paper after water removal.
But Broussonettia papyrifera owes its current importance to a negative: it is invasive. Even though this tree or shrub requires, in principle, a warm humid climate, it is robust enough to adjust to a wide variety of locations. It has become a pest in countries as diverse as Pakistan, Uganda, Ghana and the Argentinian pampas. This weed is spreading through the United States and it threatens Australia. In the former,it was introduced back in the 1620s, when sericulture was attempted in these British colonies.
The small fruit, 1.5-2 cm in length, eaten by birds and other wildlife are the primary means for dissemination. Once established, paper mulberry extends its occupation through its root system. The thickets thus grown can become up to 30 ft across.
The scientific name of any plant species honors a progenitor of sorts, often a naturalist who wrote an early description. It refers in this case to the Frenchman Pierre Broussonet (1761-1807). Broussonet, however, is remembered in the name of the mulberry tree, for an action he carried out, not for a text he wrote.
The paper mulberry has distinct sexes, on separate trees. The female tree bears ball-shaped clusters of flowers. The male tree bears catkins.
Broussonet took a male tree from a garden in Scotland and introduced it to Paris where a female tree was growing, ensuring fertilization and the attendant description of the ensuing fruit. He was responsible also for bringing back to Paris the very first Ginkgo biloba tree planted there, in the Jardin du Roi — the present Jardin des Plantes.
More importantly, Broussonet was the pioneer who extended to animals the binary classification Linnaeus introduced for plants. He did so in a comprehensive treatise he wrote on fishes.
He had, most unfortunately for him, yet another claim to fame. A stroke made him aphasic during his last years: subsequently, his speech was impaired, he was unable to say any name, whereas adjectives and verbs remained most fluently available to him. This very speech disorder, carefully observed by fellow physicians — Broussonet was an MD with an avocation for naturel history — who carefully observed his behavior and also autopsied his brain, later allowed Paul Broca (1824-1880) to locate the center of speech in the frontal lobe of the left hemisphere of the brain (in right-handed persons) — the so-called Broca area.
What a trajectory, from China to France, from helping to communicate our thoughts to a speech impediment, from ordinary to luxury paper!