THE FALLEN LEAVES
The oldest seed plants are the gymnosperms. Fossil evidence indicates they are over 200 million years old. They are non-flowering and produce naked seeds, that is seeds not enclosed in a fruiting structure. Geologically, the oldest living gymnosperm is Ginkgo biloba, a species once widespread over the earth, but probably saved from extinction by the Chinese who cultivated it in their gardens.
Other examples of gymnosperms are the pines, spruces, firs, hemlocks, yews, cypresses and larches. These are basically evergreen and cone producing. A recent fossil discovery indicates that angiosperms are only a little over l00 million years old. These fossils had flowering structures and seeds insides of a fruit as do all of our present day angiosperms.
The retention of leaves over one season shows variability in these two groups of seed plants. A special abscission layer forms at the base of the leaf where it is attached to the stem. This layer of special dividing cells interrupts the elongated stronger cells except for the tissue which supplies water to the leaf. When this water-supplying vascular tissue breaks, the leaves fall. Wind and rain hasten the fall.
At Heidelberg, a lottery is set up every year to determine who can select the date when the majority of the leaves of a 75 year old Ginkgo fall on a particular day. That usually occurs around November 10th and usually the day after a hard freeze. Some evergreens are not ever-green.
The Larch or Tamarack, native to 9 northeastern counties and to Williams and Defiance Counties of northwestern Ohio, sheds its needle-like leaves every year. This plant, a northern species can be found in a boggy habitat above 3,000 feet in the Mid-Appalachian Mountains. European Larches can be seen on the Heidelberg Campus west of the Library and along Coe Street in Hedges-Boyer Park. A healthy Bald Cypress once grew between Founders Hall and the Administration Building at Heidelberg but was killed as a result of the blizzard of 1979.
It had beautiful feathery-like leaves that were shed each fall. It is native to southeastern U. S. and extends as far north as Virginia. Pines usually shed their three year old needles at a certain time each year. Pine branches except for those at the tip are devoid of needles. Spruces, hemlocks and others keep their leaves that are five or more years old.
Most of the branches except for the older parts are covered with leaves. This is a reason why they make good Christmas wreaths. The evergreens will lose water from their leaves during balmy days in the winter and are unable to absorb water from the frozen ground. Evergreens, particularly the young ones, should be well watered each late fall before the ground freezes.
They can be winter-killed or damaged, particularly on the windward side, if too stressed. A wind barrier can help young trees. Deciduous trees solve their winter water problem by shedding their leaves and developing a cork like layer over the leaf scar. Those woody angiosperms that retain their leaves like Rhododendron, have developed physiological and physical devices that control moisture loss.
The edges of their leaves curl inward and droop during the winter months. The live oaks of the southeastern states renew their leaves each February. The leaves of many tropical trees are gradually replaced. However, some species lose all their leaves at a given time each year. The Ceiba, or kapok tree, loses all of its leaves two times a year. New leaves develop very rapidly after the old ones fall.
Each tree species has a leaf scar of a particular shape and size. Sometimes a hand lens is necessary to see the arrangement and number of vascular bundle scars within the leaf scar. All maples have a V-shaped leaf scar and three vascular bundle scars. There are over l00 woody angiosperm species in Seneca County.
Most can be identified to the species with a hand lens and a winter tree reference and a piece of a 2-year-old stem when the leaves are not present. Most angiosperm trees in Seneca County are without leaves about 6 months of the year.