y6 READINGS IN BIOLOGICAL SCIENCE 



THE FINEST SHOW ON EARTH * 

 EDWIN B. MATZKE 



If you were given the opportunity of viewing again one single scene 

 from all those that you have enjoyed, that constitute memory's picture 

 book of the past, which would you choose? Would it be one which por- 

 trayed the awe-inspiring grandeur of a total eclipse of the sun or possibly 

 one which recorded the glowing, changing colors of an alpine sunset? Or 

 would you turn to a page showing the brilliant patterns of a New England 

 landscape when the days are growing short and your breath rises lazily 

 before you? While a total eclipse and a sunset are passing fancies on the 

 part of nature, lasting for moments or minutes at the most, autumn foliage 

 in eastern North America clothes the hills in brilliant vestments for weeks 

 at a time. 



To what are these colors of autumn due? The ordinary cells of plants 

 owe their green to two pigments, called "chlorophyll «" and "chloro- 

 phyll Z?." These can be extracted from the leaf with warm alcohol, and 

 the solution becomes a deep rich green, a green that through long associa- 

 tion with us on this earth has become soothing and restful to our eyes; no 

 color seems quite so pleasing as that of chlorophyll, no color is so impor- 

 tant, since only plants that contain this can manufacture foods, for them- 

 selves and for us. In addition to the two chlorphylls, two other pigments 

 are also present in ordinary leaves; these vary from yellow to reddish or- 

 ange. One of these, carotene, is common in carrots — a scientific justifica- 

 tion, it has been suggested, that "carrots are good for the complexion." 

 The yellow and orange pigments are less complex, chemically, than the 

 green chlorophylls, and they are also more stable. When the weather gets 

 cold in the fall, the green colors, which break down more easily, tend to 

 disappear, and then the yellow and orange, which have been present all 

 along but masked by the others, become visible. These are largely though 

 not entirely responsible for the golden tints of autumn. These four pig- 

 ments together constitute only a minute fraction of the fresh weight of the 

 leaves — about twenty-six hundredths of one percent — a very small frac- 

 tion when we consider how important they are, especially the chloro- 

 phylls. There is another group of soluble yellow pigments which are 

 not very significant in fall coloration. 



Most striking of the colors of autumn are the reds. These are due to 

 an entirely different group of substances, called the anthocyanins, com- 

 pounds associated with sugars, dissolved in the cells of the leaves. These 

 vary from the brightest scarlet through all the shades of red and magenta 

 to the deep blues and purples found in some leaves and many flowers. 



• Reprinted by permission of the Scientific Monthly, American Association for the 

 Advancement of Science. Copyright 1942. 



