The Nikon MicroscopyU confocal microscopy image gallery was created with a PCM-2000 confocal scanning system interfaced to a Nikon Eclipse E600 upright microscope. Images were recorded in successive z-axis serial sections with C-Imaging Systems software with excitation illumination provided by an argon-ion and/or a helium-neon laser.

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Each new leaf forms a specialized layer of cells called an abscission that is located between the leaf and the stem and is responsible for the changing colors of leaves in the fall season. The abscission layer, which is also present in flowers and fruits, is comprised of minute tubules designed to transport water to the leaf and carry carbohydrates back into the tree. In the autumn, cells in the abscission are triggered by plant hormones to secrete a waxy substance termed suberin and begin to swell, reducing the amount of nutrients and water that flow through the tubes. Without fresh raw materials, leaves cannot produce chlorophyll and the green color, which dominates trees throughout the spring and summer, fades to reveal the color of pigments that have been present in the leaf all along, such as orange and bright yellow. Each leaf may display a variety of different colors during various times of the year before eventually depleting all reserves and dropping from the tree. This transformation of color is caused by internal changes occurring between the varying amounts of different pigments.

Changes in abscission layer, which produces the wide spectrum of colors ranging from yellow to red, are activated by temperature and the length of the night (the time that sunlight is not available), called the photoperiod. A hard frost can prevent the leaf from completing its natural cycle and simply cause it to die and turn brown. Typically, the color change in leaves initiates at the outer edges of the tree and progresses inward.