Inventory of Plausible Biomes

The Inventory of Plausible Biomes is the Tower's authoritative register of enclosed environments deemed sufficiently coherent to be maintained, heated, patrolled, and defended against revision. It is administered jointly by the Bureau of Static Inventory and the Department of Speculative Biology, a division of authority that has never been resolved and is now considered part of the instrument itself. The Inventory does not record every biome in the Tower; it records only those whose existence the Tower has agreed to keep asserting in writing. At the time of the last general recension it listed 1,144 entries, of which 39 are marked "provisionally plausible," 11 "contested," and one, Epsilon-9, "plausible, pending."

Origin and the Recension of 1873

The Inventory was first consolidated under the Second Concordance, Clause VII, which required that any biome subjected to continuous occupation be entered in a single register so that its weather could be predicted, its jurisdiction assigned, and its losses apportioned. Prior to this, biomes were catalogued in the floors on which they occurred, with the consequence that adjoining floors often disagreed about whether the same climate existed. The Recension of 1873, carried out over a period of nineteen months by clerks working in shifts, reconciled these accounts and produced the first numbered register.

The recension established the practice of grading each entry by plausibility rather than by habitability. This distinction was deliberate. A biome may be entirely lethal and still be plausible, provided its lethality is consistent; conversely, a temperate meadow with one unaccountable anomaly is entered as contested no matter how pleasant it is to visit. The measure of an entry's stability is expressed in Niven, defined elsewhere as the resistance to one further plausible amendment. Entries below 0.4 Nv are inspected quarterly.

Procedure and the Problem of Mingling

Entry to the Inventory is by petition. A petition must specify the biome's extent in floors, its atmospheric budget, its characteristic organisms, and the manner in which it is bounded. The last of these has consumed more clerical hours than the other three combined, owing to the strict prohibition, under the Second Concordance, Addendum 3 of Clause VII, against the unlicensed mingling of biomes — an addendum adopted after the Incident of the Wandering Addendum, in which an unsealed boundary caused the fog of one entry to be recorded, for six days, as falling on a floor eleven levels distant. The remedy adopted at the time was the Taxonomic Isolation Seal, which remains in use and is inspected on the same schedule as the entries it protects.

Plausibility is assessed against the Axiom of Material Coherence, which requires that every feature of an entry be supportable by the remainder of the entry. The Department of Speculative Biology has repeatedly argued that this test is too weak, and has pressed for the use of the Grand Taxonomy as an external check; the Bureau of Static Inventory has replied, in a memorandum of 4402, that "a biome may be plausible without being inhabited, and the reverse is not the Bureau's concern" (Memorandum 4402/14, Bureau of Static Inventory).

Epsilon-9 and the Competing Claims

The most persistent difficulty in the Inventory concerns Epsilon-9, an atmospheric biome of considerable extent whose maintenance is claimed by the Department of Speculative Biology and whose registration is claimed by the Bureau. The Department holds a standing claim over atmospheric systems adjacent to active biomes, which by its reading includes Epsilon-9 entirely; the Bureau maintains that the claim concerns adjacency and not the system itself, and has entered Epsilon-9 in the Inventory with the qualifier "pending" since 4390. No fewer than four advisory opinions have addressed the matter, including Advisory Opinion 17 (4119), which found that the qualifier was "not improper, but not a holding" — a formulation that has settled nothing.

The Lysander Beetle and the Damp Vaults

Because the Inventory governs the maintenance of the biomes it lists, it also governs the organisms held to be characteristic of them. The best-known illustration is the Lysander Beetle, endemic to the fungal biomes of Sub-level 71-A, which is entered under that floor's biome and cannot lawfully be removed from it without a boundary licence. Attempts to breed the beetle in the drier galleries, for study, have twice been halted not because the galleries were unsuitable but because the beetle's entry in the Inventory designates a biome and the galleries are designated a corridor. The beetles were returned. The corridor was re-entered as a biome and then, in 4408, re-entered as a corridor.

"Where a holding is characteristic of a biome, its removal constitutes a mingling of that biome with another, whether or not any specimen is carried, and whether or not the second biome is listed."

— Second Concordance, Addendum 3 of Clause VII

Relationship to the Inventory Proper and its Instruments

The Inventory of Plausible Biomes is a subsidiary register and is not to be confused with the Inventory itself, from which it derives its authority and to which it reports only totals. Its entries are maintained under the Ordinance of Continuous Inventory, which requires perpetual observation rather than periodic count; in practice this has meant that each listed biome is watched, and that the watching is recorded, but that the record is not always reconciled with the register. Divergence is handled through Proxy Inventory Maintenance, and where divergence is severe enough to produce a discrepancy in the total, through Inventory Echo procedures.

A minor instrument, the Probability-Weighted Manifests, is used in the field to record provisional observations in biomes whose weather prevents a fixed count. Clerks are reminded that these manifests are ephemeral and that no entry carried forward from one has ever been admitted to the Inventory without confirmation by standing observation.

Disputed Entries

The eleven contested entries are a standing embarrassment. The disagreement is not about the biomes themselves — all eleven are visited regularly and are free of anomaly for months at a time — but about the point at which instability becomes a property of a biome rather than of the record of it. The school of Phenomenological Inventory holds that an entry becomes contested when observation of the biome alters what is observed, and would transfer the eleven to the Bureau of Paradoxical Inventory; the Bureau of Static Inventory has declined to transfer them on the ground that the Paradoxical Bureau's register is not admissible as evidence in any proceeding, including its own.

The Materials Inventory convention of 4391, which resolved a similar dispute over certain holdings by recording them twice under both offices, was proposed for the biomes and rejected. It was rejected because a biome recorded twice is, in the plain reading of the Second Concordance, two biomes, and two biomes in contact require a seal. Visitors to Epsilon-9 are asked not to enter by more than one aperture on the same day.