Luminal Moss

Luminal Moss is the general catalogue designation for any bryophytic growth whose emitted light is measurable on the Luminal Gradient without the interposition of a reflective or transmissive medium. The designation covers some forty-one recognised forms, of which Creeping Phosphor-Moss and the cultivated tincture stocks of Lumen-Moss Cultivation are the most frequently handled; it does not extend to any specimen whose light is considered reflected rather than emitted, a distinction that has generated more paper than any other in the field.

All Luminal Moss falls under the direct oversight of the Guild of Luminal Regulators, which maintains separate registration for PC specimens and which first attempted to clarify the ledger by grouping luminous bryophytes into Primary, Contingent and Provisional categories in the year 3 112. The grouping survives, though the categories have been redefined four times and are no longer agreed upon even within the Guild.

Definition and the Reflected-Light Objection

The foundational definition is set out in the Manual of Luminal Gradients, which instructs assessors to establish emission using a Nocturnal Aperture shielded from all ambient light, and to record a specimen as luminal only where the aperture returns a reading unaccompanied by any luminous source in the immediate vicinity. The wording is careful; the practice is not. Aperture work on poorly sealed floors routinely records reflection as emission, and the resulting misattributions are corrected only at the next Reconciliation of Luminal Gradients, a bi-decadal procedure in which documented ratings are aligned with observed states. Between reconciliations, a misattributed specimen can be cited in support of a disputed claim for years.

The Guild of Luminal Surveyors, which measures light but does not correct it, has argued in its triennial returns that the aperture method is best understood as an instrument for confirming a reading already expected, and that specimens should be categorised by their behaviour in a room rather than by any shielded observation. The Guild of Luminal Regulators has not accepted the argument, and the two Guilds continue to publish assessments that differ by up to two bands on the same specimen.

Varieties and Cultivation

The plain wild form grows on damp masonry throughout the middle floors and requires no tending. It is the cultivated stocks that occupy the Guild's attention. The most significant is the Lumen-Moss Symbiotic Tincture, in which a phosphorescent fungal associate is bound to the moss itself, producing a light that is steadier but considerably harder to extinguish. Tincture beds must be recessed at least nine inches into the floor so that a dropped lamp cannot be mistaken for a specimen during counting.

Pruning is performed with the Moss Calipers and follows a schedule rather than a judgement; the caliper registry fixes the cutting interval, and calipers returned out of sequence are held at the equipment desk until reconciled. Moss Growth Spirelocation governs the siting of any stock permitted to develop vertically, a practice restricted since the Moss-Growth Spire Schism to floors above the eleventh gallery.

Use of Mourning Moss

Unchecked luminous growth is controlled with Mourning Moss, which darkens adjacent bryophytes by a mechanism not yet established to anyone's satisfaction and which the Guild endorses for the purpose. The endorsement is more than a century old and has never been reviewed. It requires that Mourning Moss be introduced only in measured portions, and only where a specimen's gradient reading has been certified within the preceding thirty days.

Because Mourning Moss is itself a moss, and because it does not always stop at the boundary of the infestation, sites have on occasion been recorded as cleared and subsequently found to contain no moss of any kind. The Report on the Defence of the Ninth Gallery records one such episode in the winter of 3 147, in which a Regulator-Team certified a gallery free of luminous growth and returned nine months later to find the growth restored and the Mourning Moss in a condition the report declines to describe.

Classification and the Vat Dispute

Vat-grown stocks, held in liquid humour, are classified under Clause 3 of Annex 7 to the Tenth Concordance, which distinguishes them by the shift of the specimen towards the yellow spectrum within three hours of exposure to humour. The clause has been read two ways since its promulgation. The reading favoured by the Luminal Division holds that the three hours run from first contact; the reading favoured by the Guild of Luminal Regulators holds that they run from the completion of the vat's filling, which may be days later. The difference determines whether a stock is classed as Primary or Provisionally Contingent, and so whether its light may be relied upon in a regulatory return.

"The clause states a period, not a method. Where an instrument is silent, the older practice governs."

— Tenth Concordance, Annex 7, marginal gloss of the second recension

The older practice, unfortunately, is itself disputed. A working compromise observed on most floors requires the vat to be marked at both moments and the objection noted in the margin; this satisfies neither Guild and has been in continuous use since 3 156.

Incidents

The best-remembered incident remains the misattribution of a reflected reading on the fourth basement landing, where a mirror stored beside a moss bed produced an aperture reading later found to have been used in support of an amendment to the Tenth Concordance. The amendment was withdrawn; the mirror was not. Assessors conducting Luminal Assessment on enclosed floors are now required to record the presence of any reflective surface within six feet of the specimen, a rule introduced after the landing incident and observed almost everywhere.

Incidents of the second kind arise from the moss itself. Where Luminal Moss is permitted to dry — as happened on the upper stacks during the dry winter of 3 163 — it powders, and the powder retains its light for some hours after settling. The Guild of Luminal Regulators recorded that season's floors as presenting "a general luminescence not attributable to any registered specimen," and made no further finding. The dust was swept up in the ordinary way.