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We are taught in school that the green in the leaves of a tree is from chlorophyll. Since chlorophyll is the chemical responsible for photosynthesis - the process of making food for the tree - and since it is the leaves that are green, the leaves are where the photosynthesis takes place. While this is certainly true, photosynthesis can happen anywhere there is chlorophyll in the tree.
Chlorophyll is found not only in the leaves of trees, it can also be found in the cortex - just under the outer bark layer. Therefore, photosynthesis can take place in the bark of the tree as well as the leaves. Since the surace area of the bark is much less than that of the leaves and since the bark is often shaded by the leaves and receives a lot less sun, the amount of photosynthesis happening there is not very large. But in the early spring, before the new leaves have formed, the photosynthesis in the bark can be an important factor in the tree preparing for the season ahead.
Of course, for photosynthesis to happen in the bark, sunlight must reach the chlorophyll in the cortex. Therefore, the bark layer must be very thin for this to happen. Usually this means fast growing trees or thin branches where the bark is smooth and thin.
In this activity, you will search for the trees in your yard with a green layer of chlorophyll under the outer bark. Look under both the bark in the trunk and the bark on a thin twig. You might think of making a chart to keep track of the trees you investigate. At the end of this activity, you can find a suggested chart.
Caution: This layer is very thin, so be careful not to scrape to deeply or you will scrape this layer away as well.
Try looking on both the south side and north side of the trunk. Do you see any difference?
Try looking at the twigs as well as the trunk. Do you notice any difference?
If possible, try scraping away a bit of bark from a thick-barked tree as well as thin barked trees. Do you notice any difference?
tree type bark type location diameter direction chlorophyll present