DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Beech tree leaves. Light micrograph of a section through two leaves from different parts of a common beech tree (Fagus sylvatica). Some leaves of a beech tree get the maximum exposure to sunlight whilst others get less sunlight because they are shaded; e.g. other leaves are above them. Therefore the leaves vary in their structure according to how much sunlight they receive. The lamina of a sun leaf (lower) is thicker; it has two layers of palisade mesophyll tissue and more chloroplasts. It also has a deeper spongy mesophyll layer with more chloroplasts and storage for starch, more air space for gases to get to the cells, bigger veins and xylem vessels to receive water and minerals, and bigger phloem vessels to carry food around the plant. The shade leaf.
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