Hogwarts, Subfusc and the Lowdown on Caps and Gowns
Almost everyone has donned subfusc garb on one occasion or another. This is the "graduation gown" of high school and college commencement services, and the conventional dress at Harry Potter's alma mater, Hogwarts Academy. Sixty children made temporary subfusc out of black plastic trash bags at a recent "Day at Hogwarts Academy" program at the Bluffton (South Carolina) Branch Library. But what is the origin of this all-too-familiar costume?
The website of St. Anthony's College, one of 36 colleges at Oxford, England, told its freshmen that the subfusc is "the get-up which makes you look like a penguin but makes you feel like you are part of Oxford. Tourists will ask you to be in a photo with them wearing your subfusc."
Oxford students must wear their subfusc when taking their exams. The dress (which also can be spelled "subfusk," "sub-fusc" or sub fusc") consists of mortarboard cap, gown, white shirt and white bow tie. It also is obligatory at all formal functions. 
"By a quirk of history," wrote Teresa Killian , "women may wear pants as part of the subfusc ritual (the early rule makers just did not conceive of women wearing pants, and so, did not prohibit it, one suspects)." Females may by no means wear stockings to the "Examination Schools" (places where the tests are administered); black socks and black shoes are de rigueur for all students. The "Freshers' Guide" webpage of Oxford's Kebler College clarified that women wear a black tie or ribbon with their subfusc.
Michael Olmert  wrote that academic costumes descend from the everyday medieval dress. As such, they are almost always made of black fabric, the scarlet robes of the Oxford Ph.D making a notable exception. The online Grolier Book of Knowledge added that scholars of the Middle Ages were members of the Church and wore their black ecclesiastical gowns to classes. The hoods on professors' gowns once shielded them from winter winds.
Olmert traced the mortarboard cap to the Scottish universities of the 1500s, where it was known as a cater-cap, or John Knox cap. "Cater" described the cap's four sides, and John Knox (1513-72) was the famous Scottish Protestant and religious reformer. The general term "mortarboard" dates only to 1854. Before then, the cap was known as the "square cap" or the "trencher cap" (because the headgear looked like an upside-down trencher, or serving board with a bowl on it).
James M. O'Neill  reported different story of the mortarboard's origins: It might have been introduced at Oxford in the 1200s and its shape might represent the campus quadrangle.
A less-substantiated theory dates the mortarboard back to ancient Greece, where a number of students came to a sumptuous banquet wearing sackcloths and bearing masons' mortarboards. Their teacher told the other guests that the students were so attired because "their destiny is to build. Some will build cities -- perhaps one may even build an empire. But all will be builders on the solid foundation of knowledge."
The University of Phoenix has a web page devoted to a number of "Cap and Gown Etiquette" FAQs. As for the wearing of tassels, the page said that these "are worn over the left or right temple depending on the school's tradition. All graduates should wear the tassel on the same side for uniformity. Some schools switch the tassel from one side to the other in unison - after all diplomas have been received."
New high school graduates have been marching down the aisle in cap and gown for slightly less than a century. The custom began in 1908.
The Oxford English Dictionary entry for "subfusc" gave the Latin adjective "subfuscus" as the source word, It is a compound of sub (under, close to, up to, toward) and fuscus (dark, dusky). Also, a rarely-used English adjective, "subfuscous," means "of a dark or somber hue; dusky; swarthy."
The first college of Oxford University was established in 1249, with beginnings in what The Columbia Encyclopedia called "groups of young scholars who gathered around the learned monks and teachers of the town" earlier in the century. Oxford and its traditions have survived almost intact through the centuries. During World War II, the university found an unlikely protector in Adolf Hitler, whose scheme it was to make Oxford his European capital once he had conquered Great Britain. Accordingly, he instructed his bombers to spare the town and its campus in their raids over England.
 Fodor's Great Britain. New York: D. McKay, 2005.
 Killian, Teresa."The Hither and Thither of Exams." The America's Intelligence Wire, Dec. 30, 2002.
 Olmert, Michael."Points of Origin: History of Graduation Ceremonies"Smithsonian, June 1986.
 O'Neill,James M."The Circumstances Behind the Pomp Are Centuries Old." The Philadelphia Inquirer, May 16, 2001.