Unlike the bright colors of flowers, which attract pollinators, or the bright "Warning Colors" of many kinds of animals, the bright colors of fall foliage are a byproduct of chemical changes as the trees start to go dormant. These colors have no apparent biological function or significance.
The most intense of fall color occurs in in areas such as New England, with almost pure stands of a few types of trees, such as maples and birches, that all turn color at the same time during the short fall season.
The most varied fall color, as well as the longest lasting, occurs in areas such as the southern Appalachians, where a dozen or more kinds of trees may change color at slightly different times over the longer fall season.
The change in day length (photoperiod) that causes the chemical changes in the trees leading to the bright colors starts June 21, the longest day of the year, as the sun starts to move south and the days become shorter.
Leaves have just as much yellow pigment (xanthophyll) in July when they are green as they do in October when they are yellow. In July the darker green pigment (chlorophyll) masks the yellow color.
Bright sunlight is essential for the production of the red (anthocyanin) pigment in the fall leaves: if a black mask is placed on part of a leaf before it turns red, the part of the leaf under the mask will turn yellow while the exposed part will turn red.
LONG TERM CONSTRUCTION
At the age of 26, Michelangelo began sculpting his monumental statue of David. He finished it seventeen months later, in January, 1504.
Although construction of the Notre Dame Cathedral in Strasbourg started in 1015, it was not until 1439 that the spire was completed.
The Hoover Dam is 726 feet tall and 660 feet thick at its base. Enough rock was excavated in its construction to build the Great Wall of China.
The estimated weight of the Great Pyramid of Egypt is 6,648,000 tons.
The great Gothic cathedral of Milan was started in 1386, and wasn’t completed until 1805.
The largest stained-glass window in the world is at Kennedy International Airport in New York City. It can be seen on the American Airlines terminal building and measures 300 feet long by 23 feet high.
INTERESTING BUILDING TECHNIQUES
The Incas considered bridges to be so sacred that anyone who tampered with one was put to death. Among the most impressive Inca bridges were the chacas, or rope bridges, that spanned great distances over gorges and rivers.
A bridge built in Lima, Peru around 1610 was made of mortar that was mixed not with water but with the whites of 10,000 eggs. The bridge, appropriately called the Bridge of Eggs, is still standing today.
Japanese farmers, after removing the hulls from their rice crop and sorting out the white kernels, take the hulls from the leftover rice, mix them into a kind of paste, mold the substance into brick-shaped blocks, and build houses with them.
The Column of Trajan, built in 113 A.D. to commemorate the Roman emperor Trajan's victories against the Dacian tribes of the lower Danube, contains a continuous frieze a yard wide and 218 feet long in which more than 2,500 human figures as well as hundreds of boats, horses, vehicles, and pieces of military equipment are depicted. This great column, still standing today, rises 128 feet from the ground, is 12 feet thick at the base, and is made entirely of gilded bronze.
The Escorial, the famous palace located outside Madrid, was built in the shape of a gridiron because Saint Lawrence, to whom the palace was dedicated, was roasted on one.
The base of the Great Pyramid in Egypt is large enough to cover ten football fields. According to the Greek historian Herodotus, it took 400,000 men twenty years to construct this great monument.