I think we have crossed wires, George - I was referring to the reference to Morespider's "sinks", tongue firmly in cheek; but remembering the tragic day my Dad took me up to the Whitestone pond to try out the sailing trimaran he'd made from solid oak... well, wood's supposed to float, innit???
I did submit an article on the use of peeled bramble stem* for fluted float bodies, but it never appeared - the chaos of the "move", I think.
The elder pith I used was liberated from microbiology stores when they realised they'd probably never hand-cut another tissue section, since when I've not been able to find any more - every bit of elder I try has about a quarter of an inch of pith immoveably welded to uncleaveable bark!
Any hints on what to look for in an Elder shoot? (Before you cut it, I mean!)
The stuff Watkins& Doncaster used to sell for microbiology was about half an inch diameter, gorgeous stuff.
* the really ferocious 5/8" stuff - you peel the thorns and outer bark off, and the inner bark dries to a hard coating. It will bear experimenting, I think.