density of points. The pitch $h(s)$ must vary linearly with $s$. Also, the tangent cone is not capped, in fact, it can only end as a cylinder of seeds-loaded branches.

Thus, as summarized in one sequence $c(s)$ of grains and grain boundaries $[,,]$,\
$..., 6,6,[5,5,5,5,5,6,6,6,7,7,7,7,7],[5,5,5,6,6,7,7,7],6,6,...6,[5,5,6,7,7],6,6,6...$.\
Successive grains are the spherical phyllotaxis $(13,8,5)$, the mast $(5,3,2)$ on a cone and the seeds-loaded branches $(3,2,1)$ on a cylinder.

Conclusions
===========

We have shown that the phyllotactic organization into parastichies and grain boundaries is robust. It survives cell disappearance and persists through growth. It accommodates shear stresses naturally. This is indeed the essential property of soft matter in general, and of foam in particular. Here the foam is not random, but organized into layers [@oguey]. A grain boundary is singularly effective as it is a layer of square cells joining at critical four-corner vertices, ready to flip under shear one way or the other. The disappearance of the first pentagonal cell that leaves invariant the organization into parastichies, is the other crucial agent of the malleability of the structure.

This paper has been written as a tribute to Professor Dominique Langevin on her official retirement. NR is grateful to F. Rothen and A.-J. 