1. External Form of a Woody Twig

External Form of a Woody Twig

A woody twig, or stem, is an axis with leaves attached. The leaves are arranged in various ways around and on the axis. You may hear them described as an alternate, or alternately arranged, opposite or oppositely arranged, or if they are found in groups of three or more they may be referred to as whorled. The region, just a general area in this case, where the leaves attach to the stem are called nodes. The region of stem between two nodes is called the internode. The leaf blade is attached to the stem via a stalk called the petiole

In the angle, or axil, formed between the petiole and the stem you will find the axillary bud. Axillary refers to a structure that forms an armpit, just for trivia’s sake. These buds can become new branches or they may have tissues that will form into flowers for the next season. Most buds are protected by bud scales which fall off as bud tissue begins to grow. In general, at the tip of a twig a terminal (or ending) bud is present. It is larger than the axillary buds and produces tissues to extend twig length during the growing season. When the bud scales of a terminal bud fall off they leave scars on the twig. You can calculate the age of a twig by counting up the terminal bud scale scars. There are other scars on twigs that may look like terminal bud scars that are left by paired appendages called stipules which are found at the base of a petiole in the axil.

Trees and shrubs that lose their leaves every year, deciduous plants, have characteristic leaf scars with dormant, or not active, axillary buds directly above them. Sometimes tiny bundle scars can be seen. These scars are found in the leaf scar and mark the location of food and water-conducting tissues. The shape and arrangement of the bundle scars can help distinguish deciduous trees in the winter months when the leaf structures are absent.