Shape Thesaurus Entry: Tube

Natural:

Grass stems
Straw
Reeds
Burrows
Intestines
Valves (heart, etc)
Veins
Esophagus
Nostrils
Bamboo
Lava tubes
Chives
Green onion stems
Dust devils
Tornadoes
Coral
Porcupine quills
Sea urchin spines

Man-made:

Straw
Culverts
Pipes (copper, metal, PVC)
A pencil with no lead
A pen with no ink chamber
Flashlight
Tunnel (subway, mine shafts, etc)
Underpass
Tube slides/Water slides
IV tube
Dental Suction tool
Pop can
Thermos
Test tube
Florescent lights
Rigatoni, macaroni shells
Candy straws
Exhaust muffler
Chinese finger trap
Doctor's needle
Blow gun
Pistol Barrel
Garden hose
Eye dropper
Sewers

Synonyms:

cylinder, column, pipe, hollow, duct, pipeline

Describing a shape is best done in as few words as possible. Think of the shape as a camera snap shot--you want to capture the gist of what you mean as soon as possible so you can get on with other related (and more important) detail, and the action happening in the scene

A weak example:

Rot had eaten the core of the giant oak stump, turning it into a test tube to hold the rain fall.

What's wrong with this example?

In a natural setting, the visual should not only be apt, but also complementary. Creating a comparison to a scientific implement in this case sanitizes the descriptive imagery.

A strong example:

Rot had eaten the core of the giant oak stump, leaving a circular hollow set in its heart--a perfect home for forest creatures to nest in.

Why does this work?

This description is balanced in keeping with the natural setting.