Tuesday

Raven holds the seedling's first leaf up to the window. "What do you notice about the light coming through?"

"Greenish," Rocket says. "So the leaf lets green through. Or bounces it. Where does the rest go?"

Nova projects a rainbow strip on the sill. "Chlorophyll absorbs light from both ends," she says. "Red and blue."

"And not green," Rocket says slowly. "So green is the color it does not use. That is the color we see."

Raven lifts the celery stalk and points at the tiny dots on its cut end. "Now the second puzzle. Water pipes."

"Pipes in a plant?" Rocket laughs. Nova hums. "Bundles of hollow cells, running the whole length of the stalk."

Pigments absorb some colors of light. The open text Biology says pigments reflect or transmit the colors they cannot absorb.

Chlorophyll a absorbs light from either end of the visible spectrum, blue and red, but not green. Green is reflected or transmitted.

Because the green light bounces back to your eyes, chlorophyll appears green. That is why most leaves are green.

Other pigments called carotenoids absorb blue and reflect yellow, orange and red. One carotenoid gives carrots their orange color.

Plants have a tissue called xylem that conducts water. Its water-carrying cells are joined end to end, and water moves from one to the next up the plant.

Xylem and another tissue, phloem, run in strands called vascular bundles up and down the length of a stem.

In a leaf, the vascular tissue forms veins. Most leaves have a midrib that branches to each side to produce the veins.

What pulls the water up? Water evaporates from the leaf surface, a process called transpiration. That loss pulls water up from the roots.

The strings in a celery stalk are a different tissue that gives support. The water pipes are the small dots at the cut end.

Sharp thinking. Tomorrow is Windowsill Lab: celery in tinted water and leaf veins under the hand lens.