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become visible. If no yellow pigment is present, the leaves turn brown.
The development of orange, red, and purple is not quite so easy. To secure these colors, the leaves must produce another pigment called anthocyanin.
The particular shade of red, orange or purple which is developed by anthocyanin is related to the acid or alkaline condition of the sap of the plant.
If the sap is acid the color will be orange or red. With neutral sap the pigment is light purple. When the sap is alkaline, a dark purple or blue color is evident.
The amount of anthocyanic pigment produced is dependent on the accumulation of sugars and tannins. During warm sunny weather, much sugar is manufactured in the leaves.
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When the autumn nights are cool, with temperatures below 45 degrees, the sugars and tannins do not move into the branches for storage. Thus, more remains in the leaves to be converted into anthocyanins, with the resulting vivid foliage color.
If the weather during the fall is quite cloudy, sugar production is reduced. If the nights remain warm, the sugars will move to the
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