Underground plant includes all the telecommunications equipment installed in underground structures such as utility holes, Controlled Environment Vaults (CEVs), and ducts, along with associated hardware. Underground plant can be exposed to waters containing water-soluble salts of the native soil. Utility holes often show evidence of corrosion of support hardware and bonding ribbons that is caused by sulfate-reducing bacteria. The environment in utility holes and ducts can be made corrosive by man-made chemicals such as industrial effluent, fertilizers, and de-icing salts. Protective plastic coatings and cable jackets can rapidly deteriorate from leaking steam pipes present in many urban areas and from gasoline leaking from underground storage tanks.
The most aggressive contributor to corrosion of underground plant is dc stray current from electrified rail transportation systems, cathodic protection rectifiers, or welding and mining operations. Although such dc currents are mostly dealt with “after the fact” using protective systems (e.g., low resistance bonds, reverse current switches, cathodic protection), some of the protection has to be included at the manufacturing stage. This protection may include insulating covers on cable shields, or nonmetallic components or coatings for apparatus
1. Leaves are arranged isobilaterally, i.e., both surfaces are similar.
2. The venation (arrangement of veins and veins on the lamina) is parallel. In monocots veins run parallel to each other from base to the tip of the lamina. Veins connecting the adjacent longitudinal veins are inconspicuous.
3. Leaves are usually long and narrow, running parallel to the stem.
4. Leaves are mostly simple.
5. Leaf sheath (expansion of leaf base into a broad sheath) is usually present.
1. Leaves are arranged dorsiventrally, i.e., upper and lower surfaces are distinctly different.
2. In dicot leaves, venation is reticulate, i.e., irregularly distributed to form a network.
3. In most dicots, the leaf base bears two lateral appendages called stipules.
4. Leaves are either simple or pinnately compound.
5. Leaf sheath is usually absent.
Identifying features of flower:
1. The reproductive part of an angiosperm (higher) plant is flower, which develops from floral buds.
2. The flower is considered to be a modified shoot.
3. The stalk of the flower is called pedicel and the tip of the pedicel continues as an enlarged axis called thalamus or receptacle.
4. All the floral parts are arranged on the thalamus in a definite sequence.
5. A typical flower consists of four sets of floral parts, or whorls: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels).
6. The first two whorls, i.e., calyx and corolla are not directly involved in reproduction and are called accessory whorls.
7. The inner two whorls, i.e., androecium and gynoecium are directly concerned with sexual reproduction and are called essential whorls.
8. Sepals form the outermost whorl called calyx. They are usually green and leaf like, and arise at the base of the flower.
9. Petals form the corolla. They are generally brightly coloured and sometimes fragrant to attract insects.
10. The third whorl androeciunt is the male reproductive part of the flower and consists of stamens. Each stamen consists of a slender filament and an anther at the tip.
11. Gynoecium, or pistil, is the centrally placed fourth whorl which bears the female reproductive organ called carpel. Each pistil consists of a basal swollen ovary, a narrow stalk-like style, and stigma at the tip. The ovary contains one or many ovules.
1. Calyx and corolla are not distinct in monocot flowers. Instead, perianth is present which is composed of tepals.
2. In monocots, flowers appear in clusters.
3. The flower is typically trimerous (each whorl is in multiple of three).
4. Stamens are usually versatile, i.e., filament is attached to the back of anther at a point only.
1. Dicot flowers usually have distinct floral parts, i.e., calyx, corolla, androecium and gynoecium.
2. Calyx is composed of sepals, and corolla is composed of petals.
3. Flower is mostly pentamerous (each whorl in multiple of five), sometimes tetramerous (each whorl in multiple of four).
4. In dicots, flowers usually appear separately.
5. Stamens are usually basified, i.e., filament is attached to the base of the anther.