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A fallen leaf is practically devoid of food substances that are of 

 immediate use to a plant. The skeleton of the leaf is left, to- 

 gether with certain residue substances, most of which are insolu- 

 ble, in the sap of plants. It is due to various physical and chem- 

 ical changes in the residue or waste products that the autumn 

 colors in foliage develop. The yellows are chiefly derived from 

 the green pigments that prevail during summer. The residue of 

 sap pigments gives the reds, and these are influenced greatly by 

 kinds and amounts of acids that are present. 



Light is an important factor in the development of autumn 

 colors. A leaf of the red maple or of the sumac develops no 

 flaming red or rich yellow coloration if artificially darkened just 

 before it is about to change in color. If a part of a leaf is cov- 

 ered, that part remains greenish and changes to dull brown while 

 the rest of the leaf changes to rich golden or crimson. Dull 

 cloudy periods of weather are not productive of the most bril- 

 liant colorings. 



It is sometimes claimed that heavy frosts are necessary for the 

 development of autumn colorings. Throughout the more north- 

 ern states there is usually a heavy killing frost early in Septem- 

 ber or even in August. No doubt such a frost hastens the color 

 changes and the fall of leaves. But here about New York City, 

 there is seldom a killing frost until late in October. The foliage 

 of many of our trees, shrubs, and herbs passes through brilliant 

 colors and the leaves fall before there is a freezing temperature. 



Evergreen trees drop a crop of leaves each year quite as do 

 deciduous trees. The difference is that they do not drop all 

 their leaves. Autumn colors develop on the crop that is to fall, 

 but these are usually the more delicate and subdued shades of 

 yellow and brown. Autumn colorings are especially conspicuous 

 in the white pine. 



It is, perhaps, correct to say that nowhere on the earth are 

 autumnal colorings better than in the region about New York 

 City. Here there is a wealth of deciduous trees and shrubs that 

 possess pigments which give the color changes. The weather con- 

 ditions in autumn often give many clear, cloudless days with 

 bright sunlight. The change from a moist warm summer favor- 

 able to the activity of plants to a cool autumn with temperature 

 unfavorable to leaf activity and life is rather abrupt. 



