Beckon trunk
From Wikipedia, the free encyclopedia
| Anatomy | |
|---|---|
| Part of | Beckon |
| Position | Between the root crown and the bulb |
| Contains | Spine, gas cells, gas glands, vent pores |
| Pressure | 1.5–3 bar (Adapted) |
The trunk of a Beckon is the column of its body between the root crown and the bulb. It is built around a flexible spine, packed with sealed cells held at pressure, wrapped in fibre and coated in near-black light-gathering tissue and membrane gel. In the Adapted Beckon and the two larger species the cells hold sulfur hexafluoride; in the Primitive Beckon they hold water. The trunk contains no wood and no bone.
Spine
The spine is a column of tough, flexible fibre running from the root crown, below ground, to the base of the bulb. It carries the main blood vessels and the main nerve cord, and contains no mineral. The spine bends under load without breaking, and is the part of a Beckon most often recovered intact after it has been burned.
The spine cannot hold the Beckon upright alone. The pressurised cells around it brace it along its whole length and keep it from buckling, on the principle of inflatable beams built around a strut. A Beckon that loses pressure sags as the spine bends.
Gas cells
The cells are sealed compartments packed around the spine in the arrangement of a closed-cell foam. They range from a few centimetres across in small Beckons to about a metre in the largest on Earth. Their walls are living tissue, crossed by blood vessels that branch from the spine to the outer layers, and lined with the gas glands that fill them.
In an Adapted Beckon the cells hold sulfur hexafluoride at 1.5 to 3 bar, which is 0.5 to 2 bar above the surrounding air. The gas leaks through the cell walls very slowly, and a cell keeps its pressure for years. It conducts heat about half as well as air, and the cell-filled trunk insulates the Beckon. A 30-metre Adapted Beckon holds about half a tonne of the gas.
A breach empties only the cells it opens, and the membrane gel flows into the wound and seals it. Cutting through a cell also cuts the vessels that cross it, and the blood that collects in an opened cell drains out of the wound.
Outer layers
Bands of fibre wound in opposing helices around the cells take the tension of the internal pressure. Over them lies a layer of near-black tissue a few centimetres thick, which carries out luxsynthesis and holds patches of green fluorescent pigment. The membrane gel covers the whole trunk.
Vent pores
Valved pores around the base of the trunk open into the lower cells. When the outer tissue senses fire, the pores open and the cells release gas, which is about five times as dense as air and flows down over the base of the trunk and the ground around it. A Beckon can put out a small fire this way within seconds. The gas takes weeks to months to replace.
Pressure and temperature
The pressure in a gas cell falls as it cools: a cell cooled from 20 °C to −10 °C loses a tenth of its pressure. Adapted Beckons hold their bodies at 18 to 25 °C, and one that cools softens and leans. Through Overwinter an Adapted Beckon breaks down part of its gas for energy and heat, and is measurably softer by the end of the season.
Primitive Beckons
The trunk of a Primitive Beckon has the same spine and the same arrangement of cells, filled with water. It is heavier, softer and wetter than the trunk of an Adapted Beckon, and can be cut through with hand tools. Frost kills it by freezing the water in its cells.