7 8 READINGS IN BIOLOGICAL SCIENCE 



ing in soil abundantly supplied with nitrogen are often just green. In gen- 

 eral both leaves and flowers of northern plants are brightly colored, due 

 to the strong light and low temperatures. However, in 1902, Wulff, col- 

 lecting plants far above the arctic circle in Spitzbergen, found that in 

 some areas visited by northern birds and fertilized by their excreta, which 

 are rich in nitrogen, the plants were a healthy green, while the same species, 

 growing in poor soil, were brightly colored. Anthocyanins develop best 

 when the supply of nitrates is limited, even if the other conditions are fa- 

 vorable, suggesting, perhaps, that opulence and loveliness do not necessarily 

 go together. 



All these factors are important in the formation of these red-blue pig- 

 ments, known as the anthocyanins. Normally they do not act separately, 

 but through complex interrelationships, and there are exceptions to all 

 of them. Although light is so important in the formation of these sub- 

 stances, the root of the beet, which develops in the dark, is rich in antho- 

 cyanins. But in dealing with living things there are always exceptions — 

 little touches that make life worth while. 



The drab brown colors of the late autumn, those of the sere if not the 

 yellow leaf, result largely from still another group of substances, the 

 tannins, or from compounds related to them. These are the same materials 

 that are derived from the bark of certain trees, especially oak and hemlock, 

 which are used in the tanning or hardening of leather. Tannins are almost 

 universally present in the higher plants, though generally not in quantity 

 sufficient to make their extraction practicable. 



When the green pigments break down in the fall, the yellows which 

 have been present all along become visible; simultaneously the reds and 

 blues develop in certain plants so that various combinations and color 

 effects are produced. After all these have disappeared, the brown remains 

 — the brown that is destined to form a part of this good earth. 



Most important of all our trees in producing the vivid colors of autumn, 

 particularly in northeastern United States, is the sugar maple. Sometimes 

 this is just yellow, but more often red pigment is developed, especially 

 toward the tips of the branches, where the illumination is most effective. 

 This tree is the one which is tapped in the spring, and from the sap maple 

 syrup and maple sugar are obtained. It forms extensive groves, especially 

 in New England, and is really the king pin in the coloration of the north. 

 There is a brilliance to the red of the sugar maple that is unrivaled in any 

 of our other trees — a brilliance that gives it an animation and almost a 

 touch of light-heartedness that rather belies the temperament of the sturdy 

 people with whom it shares the soil. In swampy areas similar effects are 

 produced by the red maple, though it, too, may be just a bright yellow. 



Associated with the sugar maple are the birches, especially the white 

 birch. These are normally yellow in the fall, and it is common to see the 

 gold of the birches and the red of the maples standing in sharp contrast 



