An online resource based on the award-winning nature guide


Abscission Layers Forming


As the days grow shorter and the nights longer, cells near where a leaf’s stem joins a tree’s branch start to divide rapidly. This is the start of the creation of the corky layer of cells known as the abcission layer.

The annual growth of a tree ends with the formation of the abcission layer. This layer prevents the transport of materials such as carbohydrates from the leaf to the branch and it blocks the flow of minerals from the roots into the leaves. Chlorophyll, critical to the process of photosynthesis, breaks down with exposure to light and is replaced continually by the leaves during the summer. When the abcission layer forms, this is no longer possible.  The chlorophyll slowly breaks down and disappears, revealing the underlying xanthophylls (yellow pigments) and carotenoids (orange pigments) that the chlorophyll was masking. These pigments, in addition to the red pigments (anthocyanins) that are manufactured from sugars trapped in the leaf, provide us with our brilliant foliage.

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Ghosts of August

ghosts of August 190Flowering plants have a variety of ways to obtain food.  Most have chlorophyll and thus are capable of photosynthesizing their own nutrients.  A majority of these plants (90%) are also associated with mycorrhizal fungi – fungi which attach to the roots of other plants, often trees, with which most have a symbiotic relationship (both benefit). The plant receives minerals and water from the fungi, and the fungi feed on carbohydrates and other nutrients the plant produces.

Flowering plants with no chlorophyll cannot make their own food and must rely completely on other organisms for their nutrients.  Some of these parasitic plants get their nutrients directly from the roots of another plant (Beechdrops) and others (Indian Pipe and Pinesap) receive food indirectly from fungi which get their nutrients from a photosynthetic plant.  In these situations, the mycorrhizal relationship between the non-photosynthetic plant and the fungi is not mutualistic, as only the chlorophyll-lacking plant benefits. (Photo:  Indian Pipe, Monotropa uniflora (one flower per stalk) and (insert) Pinesap, Monotropa hypopitys (many flowers per stalk).

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