Lesson 1
Long, hollow, and pointy
Tracheids (say it: TRAY-kee-ids) are part of the xylem, the plant's water pipes. Each one is long and thin with pointy ends, a bit like a stretched-out spindle.
When a tracheid is finished growing, it dies and becomes hollow. Its strong wall stays. The wall has lots of small thin spots called pits.
Tracheids are a very old kind of water cell. Ferns have them, and most of the wood in a pine tree is made of them.
Try thisPress Cut it open on the 3D model to see that tracheids are hollow inside.
Lesson 2
Passing water up the plant
Tracheids line up side by side, with their pointy ends overlapping. Water moves up inside one tracheid, then slips sideways through the pits into the next one. Step by step, water climbs from the roots to the leaves.
Their thick walls also make the plant strong. That is why a pine tree can stand so tall.
Try thisPress Send water to watch water hop from one tracheid to the next through the pits.
Wow!Water can climb many meters up a tall tree without any pump. The leaves pull it up as water dries off them!