Phyllotaxis
the spirals are counted, not admired
Concept

Polar transport — where it appears

The directed movement of a hormone from cell to cell, which is what the usual mechanistic account of phyllotaxis rests on. A pump working against a concentration gradient is what that account needs, and whether it is doing what the account requires is a separate question from whether the pattern comes out.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

48 cells with a carrier that pumps auxin up the gradient. Each short line is one cell's polarisation — the neighbour it pumps towards, which is always the richer one. 10 peaks come out, at a contrast of 93%, from a start that was uniform to within 6%.

A pump that works uphill

The mechanism that actually has molecular support behind it does not use a diffusing inhibitor at all. Cells move auxin towards whichever neighbour already has more of it, which is the opposite of what transport is supposed to do — and it produces a spacing from a field that started uniform to within six per cent.

mechanism · Auxin Three disturbances, three places to get in. The rule reads its neighbours, builds a profile of the energy at every azimuth, takes the least of it, and records a position. jostle noise enters at the neighbours; placement noise enters at the record. Two of the three are upstream of the choice and can change which minimum is taken; the third is downstream and never can.

A growing organ is part of the rule

Every model in the earlier essays places primordia on a surface and then treats the surface as furniture. But the surface grows between one placement and the next, and that growth reaches the rule through the only channel it has — where the neighbours are. What looks like a boundary condition turns out to be a term in the model.

mechanism · Mechanism claims

Named alongside it

The objects these essays reach for when they reach for this one.

AuxinMechanismBasinDescription versus mechanismElongationEpitheliumHonest limitsMeristem growthModel scopeNoisePeak selectionThe placement rule

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