It must be remembered, also, that these color effects are far more brilliant and impressive when observed on a bright, sunny day and in a dry, clear atmosphere; and that the autumn foliage loses much of its attractive appearance when viewed under cloudy skies or with the air obscured by haze or dampness. One beautiful effect of the sunlight in enhancing leaf colors may be obtained by standing under a White Oak, or any tree with red leaves, and looking towards the sun. With the transmitted: light the leaves assume a far brighter color and a different hue than in reflected light: the dull, solid red changes into a fiery glow or rich wine color of marvellous beauty. In the Bronx park, near the path on the west side of the Beaver pond, stands a large White Oak which, on any bright afternoon in late October, will afford the visitor a good opportunity to study this charming revelation of nature. Still, there is a widespread belief that the autumn foliage is much brighter some years than in others, and it is conceded that this may be true to some extent.
In European countries the autumn foliage is generally inferior in brilliancy and pleasing effects to that in America. There is a lack of red, and even the yellow which predominates so largely there is dull as compared with that seen in our American forests. The Maples and Oaks are not so common, or of so great a variety. Furthermore, the American species planted there lose the brightness which they display at home, and, on the other hand, European trees grown in America fail to develop the brilliant colors of our native trees.
The inferiority of color so noticeable abroad has been attributed to a more moist condition of the atmosphere. This might apply with good reason to the British Isles and Netherlands, but hardly to sunny France, or to the South of Europe, famed for its clear Italian skies. A better reason may be found in the "greater transparency of our atmosphere, and the consequent greater intensity of light."
In his work on Autumnal Leaves,* Mr. Francis George Heath, of London, exhibits a series of twelve colored plates, in which he shows the tints of leaves collected by him in autumn from various leading species in England. The drawings are finely executed in both form and color; but, if the leaf tints have been correctly reproduced, their inferiority to the autumnal foliage in America is apparent at a glance. A comparison of the colored plates in Mr. Heath's book, with the pictures of autumn leaves shown in connection with this article, indicates plainly that, as to England at least, the leaves on American trees have colors far more brilliant, and in a greater variety.
The English botanist Hunter, in his notes on Evelyn's Silva, describes the September foliage in his vicinity as: " Plane Tree, tawny: Oak, yellowish green ; Hazel, yellow ; Sycamore, dirty brown ; Maple, pale yellow ; Ash, fine lemon ; Elm, orange; Hawthorn, tawny yellow; Cherry, red; Hornbeam, bright yellow."
Having mentioned the interior appearance of the autumn foliage in Europe, as Compared with that in certain American latitudes, it should be further noted that this difference applies to trees, and that it is not wholly true of the minor flora. In the Alps of Central Europe the shrubs and herbaceous growths above the timber line display ripened colors that, in variety and brilliancy, are unsurpassed in any country.
The direct influence of sunlight on the development of leaf color is apparent to the most casual observer. The outer leaves on a tree are the first to turn, while a leaf that is thickly shaded by others is apt to remain green until it withers and dies. Where a twig or branch presses constantly on the surface of a leal the part thus covered remains green alter the rest has turned yellow or red. If you cut your initials from tin foil or thick paper and paste them on a large leaf the letters will in time be sharply defined in green on a background of yellow or red.
* Autumnal I eaves: By Francis George Heath. London: Sampson, Low & Co. 1SS1.
Why leaves should change color is as hard to explain or understand as why the hair turns gray. The scientists who have written on the subject admit that there is much to learn about the process and its cause. The leaf cells contain rounded granules of green matter known as chlorophyll, a substance - -or mixture of substances to which the pure green color of ordinary healthy leaves is due. The appearance of any other color, such as red, yellow or purple, would indicate the presence of some substance accompanying the chlorophyll and disguising its color, or even replacing it entirely.*
The hat cells contain, also, xanthophyll, a peculiar yellow coloring matter, which remains alter the decomposition or absorption of chlorophyll; and erythrophyll, which supplies the red or crimson shades found in matured leaves.
Most of the scientific explanations of the change of color are so technical that they are of little use to the general reader, The following extract from an article in the Botanical Gazette for April, 1887, entitled, "The Autumnal Changes in Maple Leaves," by W. K. Martin and S. B. Thomas, is instinctive and interesting:
"Chlorophyll, manufactured constantly under the influence of light, is constantly undergoing decomposition by the metabolism of the cell. Under ordinary conditions, the manufacture of chlorophyll is sufficient to cover up its decomposition, and the leaf retains its green color. Under certain changed conditions, however, such as intense light or diminished vitality, the decomposition of chlorophyll exceeds its manufacture, and xanthophyll (probably one of the products of decomposition) appears. In other words, xanthophyll is being formed all the time, but only becomes apparent when the manufacture of chlorophyll is checked. The condition of intense sunlight gives us the occasional summer yellowness, while to lowered vitality must be attributed the failure ol chlorophyll manufacture in the autumn. This lower vitality is brought about by diminution ol light, lowering of temperature, and probably causes in the plant itself. Xanthophyll then stains the chlorophyll masses yellow, which were before stained green by chlorophyll, The red coloration is brought about in a very different way, as erythrophyll is manufactured in the leaf, and stains the cell sap, leaving the chlorophyll masses untouched. This red coloring matter cannot be discovered in any of the crude materials brought into the plant, or in any other part of the leaves, except sometimes in the phloeum regions of the petioles. When the leaf falls and the cell sap evaporates, ami the chlorophyll bodies die, the erythrophyll lays hold of the cell wall and solid contents and stains them. In this way dried leaves retain their red color. As erythrophyll is soluble in water, however, contact with moisture will soon cause the most of it to disappear."
* Webb's I dictionary of Chemistry.