Lattice — the series
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A head is a set of points
The nth primordium at n times an angle, and a radius of root n. Two lines of arithmetic produce a sunflower head, which is either remarkable or suspicious depending on how carefully the claim is stated — and stating it carefully is most of the work.
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A head is a lattice two dozen organs at a time
Everything said about a seed head leans on the head being a lattice, and nobody states how much of one it is. Fitted by geometry alone, a straight lattice misses a patch of radius L at radius r by L squared over four r, to within a few per cent, whatever the divergence. So a lattice good to a tenth of a spacing holds about three quarters of r organs: twenty-three at organ 900, thirty-seven at the rim of a 2,400-organ head. At about twice that, two organs land on one site and the patch has no straight lattice at all. The coordinates that straighten a cylinder do not help. Azimuth against radius squared makes the whole head exact, to the last bit a double holds.