The earliest records of glass being used by humans date back to about 2600 B.C., when the ancient Egyptians and Babylonians made beads from the material. The use of glass panes for windows, however, did not begin until the Roman Imperial period a little over 2,000 years ago. Since then, the use of glass windows for admitting light to buildings of all sizes and shapes has become almost universal.
Do you know the properties of wood ? Are you sure?
Hereby the complete list the properties of wood, explained in depth.
The use of wood by humans for fuel, shelter, weapons, and other purposes dates back into antiquity, and present uses are so numerous that it would be impossible to list in a work of this type more than the most important ones. Before discussing the economic importance of wood, let’s take a brief look at its properties.
Although most higher plants have an erect shoot system, many species have specialized stems that are modified for various functions. The overall appearance of specialized stems may differ markedly from that of the stems discussed so far, but all stems have nodes, internodes, and axillary buds; these features distinguish them from roots and leaves, which do not have them. The leaves at the nodes of these specialized stems are often small and scalelike. They are seldom green, but full-sized functioning leaves may also be produced.
Most monocots (e.g., grasses, lilies) are herbaceous plants that do not attain great size. The stems have neither a vascular cambium nor a cork cambium and thus produce no secondary vascular tissues or cork. As in herbaceous dicots, the surfaces of the stems are covered by an epidermis, but the xylem and phloem tissues produced by the procambium appear in cross section as discrete vascular bundles scattered throughout the stem instead of being arranged in a ring.
In the early stages of development, the primary tissues of stems of young herbaceous dicots, woody dicots, and conebearing trees are all arranged in a similar fashion. In woody plants, however, obvious differences begin to appear as soon as the vascular cambium and the cork cambium develop.
In general, plants that die after going from seed to maturity within one growing season (annuals) have green, herbaceous (nonwoody) stems. Most monocots are annuals, but many dicots are also annuals.
Primary xylem, primary phloem, and the pith, if present, make up a central cylinder called the stele in most younger and a few older stems and roots. The simplest form of stele, called a protostele, consists of a solid core of conducting tissues in which the phloem usually surrounds the xylem. Protosteles were common in primitive seed plants that are now extinct and are also found in whisk ferns, club mosses , and other relatives of ferns. Siphonosteles, which are tubular with pith in the center, are common in ferns.
There is an apical meristem (tissue in which cells actively divide) at the tip of each stem, and it is this meristem that contributes to an increase in the length of the stem. The apical meristem is dormant before the growing season begins.
A woody twig consists of an axis with attached leaves . If the leaves are attached to the twig alternately or in a spiral around the stem, they are said to be alternate, or alternately arranged. If the leaves are attached in pairs, they are said to be opposite, or oppositely arranged, or if they are in whorls (groups of three or more), their arrangement is whorled. The area, or region (not structure), of a stem where a leaf or leaves are attached is called a node, and a stem region between nodes is called an internode. A leaf usually has a flattened blade, and in most cases is attached to the twig by a stalk called the petiole.
