As the fall season approaches leaves begin to change color, and the trees take on a new appearance which changes almost daily.
This months featured images explore the world of a fall maple leaf.
The green maple leaf has been on the tree all summer, and provided the tree with a large surface area to catch the sunlight. The chlorophyll provides the green color and uses the sunlight to generate energy for the tree.
The red leaf has lost its chlorophyll, allowing the other colors which are present in the leaf to show through. Yellow and orange colors are produced by carotenoids which are more stable than the chlorophyll, and so last longer in the leaves.
The brilliant red colors are produced by anthocyanin. This material is made only in the fall from the last drops of sugar trapped in the dying leaves.
The final brown color of the leaves in late fall is due to the presence of tannin which has a bitter taste, and may discourage animals from eating the leaves (at least until winter makes them REALLY hungry)
To our eyes these two leaves are obviously very different, but do they look different through the microscope ? In the optical microscope, the leaf is magnified about 100 times, and we can see areas that look green, and areas that took red, showing that the chlorophyll does not all disappear at once.
The texture of the leaf is not smooth, but appears somewhat knobbly.
In the Scanning electron microscope the images appear black-and-white. There is no direct color information. The surface texture of the leaf can be clearly seen here. The image from the red leaf (on the left here) and the green leaf (on the right) appear very similar. So even though the colors of the leaves are very different - because the chemistry in the leaves is different - the structure of the leaves is the same.
Below are three more images from the underside of the fall-colored leaf. The first one shows a grain of pollen less than one tenth of the width of a human hair, which has stuck to the leaf surface. In the middle are some worm-like threads running across the leaf surface. These are probably from a fungus which is living on the leaf. On the right an insect wing scale has got caught on the threads of a cocoon which was spun under the leaf to protect another insect, which is now long gone.
All of these were found in a couple of very small areas 5 millimeters square on the underside of the leaf. Just imagine what other mysterious things might have been under the rest of the leaf, ... or on another leaf. Better yet, go and look for yourself.
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Last Update: 10/8/96