Wachs-tube (growth tube)
Not the common reading of this. However, a "growth tube" or "growing tube" might be an implement in some specialized context. But note that such compounds might also be formed with 'Wuchs-', perhaps even preferentially so.
Therefore, reading 'Wachs-' as "wax", as Otto pointed out, is probably better.
A./
PS: If you search for this word and pair it with "Wachs", you will see a long list of sites discussing Wachs-tube vs Wachstube.
