Beckon bulb

The bulb, or Assecula Bulbus, is the crown of a Beckon and holds most of its organs: the heart, the digestive and filtering organs, the nerve centre and the organ that makes the eggs of field organisms. Its outer tissue is the most active site of luxsynthesis in the body and the source of most of a Beckon's green glow. The bulb is not pressurised, has no gas cells around it, and is the most vulnerable part of a Beckon at every size.

On a 30-metre Adapted Beckon the bulb is between 1.5 and 3 metres across. The bulb of the Supreme Beckon of the Iris is kilometres across.

Structure

The bulb sits on the top of the spine, and the main blood vessels and nerve cord enter it from below. Its wall is a layer of near-black light-gathering tissue under the transparent membrane gel. Patches of fluorescent pigment in the wall glow green, more brightly as the bulb's activity rises. The tendrils grow from a ring around its base.

Inside, the organs lie in a body of soft tissue and blood, with no internal skeleton. The bulb is braced only by its own tissue and by the top of the spine.

Organs

Heart

The heart is the largest organ in the bulb. It contracts once every two to five minutes and drives the circulation of the whole organism, including its root mat.

Digestive organ

Food reaches the bulb already broken down by the root mat, which digests organic matter outside the body. The digestive organ reduces it to the materials the production organ builds with. Most of the material comes from field organisms that return to the Beckon and are reabsorbed into its ground with the biomass they have eaten.

Filtering organ

Every fluid entering from the root mat passes through the filtering organ before it reaches the rest of the body. The organ removes toxins and metals from the blood and stores them, and poisons applied to infested soil have little effect on a Beckon. Substances injected into the trunk reach the body's tissue before they pass through it.

Nerve centre

The bulb holds the largest concentration of nerve tissue in a Beckon. The nerve centre stores the blueprints from which the Beckon produces organisms, in chemical form, and receives revisions of them through the Dispatcher network. It controls the heart, the gas glands, venting and body temperature, and relays signals between the field organisms around the Beckon and the Beckons above it in the chain of command. A main nerve cord runs down the spine, and nerve fibres run out through the tendrils and the root mat.

Production organ

The production organ makes the eggs from which field organisms develop. Eggs pass down the spine into brood chambers in the root mat, where they grow on stored biomass and emerge from the ground. A Dispatcher connected to the same mat takes in finished organisms and stores them, and a Beckon with a Dispatcher produces organisms much faster than one without.

Behaviour

The tendrils around the bulb move slowly, by shifting pressure between their cells. In hard cold they fold over the bulb and hold in its heat. The glow of the bulb is used in the field as a measure of how active the Beckon is.

Vulnerability

The bulb lacks the gas-filled cells that brace and insulate the trunk, and damage to it reaches the organs directly. Its blood supply runs through the spine, and cutting the vessels of the trunk lowers the pressure of the blood reaching it. Military doctrine against Beckons of every size directs fire at the bulb.

In Vagrants

Each Vagrant carries an internal bulb, formed when the Vagrant came into being. Its glow, like the Vagrant's blood, is the colour of the Vagrant's own hive.

See also

• Beckon anatomy
• Beckon heart
• Luxsynthesis