plant parts

924

Trees with yellow leaves
Although we have had several freezes, the leaves here are just starting to change. Every year, the leaves start changing colors in the North first, and then the color change spreads South. This is not due to the temperature. What causes it?

936

Onion cells
These are onion cells, photographed through my microscope at 40X. Why do onions make your eyes water when you cut them?

949

leaves in snow
The mustard plants in my garden are still green, in spite of sub zero temperatures and snow. How do they survive when most of the other plants have not?

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