Page:Popular Science Monthly Volume 24.djvu/570

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Messrs. Editors:

HAVING been a regular reader of "The Popular Science Monthly" from its commencement, I have, of course, noticed the various articles having reference to the value of the concentric rings in determining the age of trees which from time to time have appeared in its columns, the last of which, in your August issue, induces me to give you the result of my observations upon this subject. I have had my attention directed to it during a residence of over forty years in Florida, during which my views as to the value of the rings in determining the age of trees have undergone a change. For the first few years my efforts were directed toward securing a grateful shade for the streets of the city of Jacksonville, and for this purpose the water-oak was selected on account of its beauty, symmetry of form, and rapid growth. And now the appellation of "Forest City," applied to it by visitors, is in no sense inappropriate, for many of the older trees have attained a size which in the State of New York, whence I came, would have required a hundred years to reach. Strangers from the North are apt to overestimate the age of our trees, and the number of rings presented appears to confirm in many instances the correctness of their estimate. When first called upon to account for the discrepancy shown by the rings, and the known age of the tree, I was perplexed and at a loss to find a satisfactory solution of the problem. But, having from my first arrival here kept a careful record of the weather, an analysis of my tables, a comparison with the record made by Nature on her infallible tablets in the trees furnished me the key to it.

Here, as well as at the North, the cold of winter puts a stop to vegetable growth, and in all exogenous trees a concentric ring will be formed, embracing all woody matter deposited since the preceding stop to its growth; but here in this climate causes are in operation that frequently produce as complete a stop to vegetable growth as does the cold of winter.

Our spring begins in February, when growth commences a new deposit between the bark and wood, but often (not always) there comes so severe a drought during late spring and early summer as to produce as full and complete a stop to vegetable growth as does the cold of winter; immediately after comes on our rainy season, generally

about the middle or last of June, producing a rapid and luxuriant growth, which continues until winter again puts a stop to it. Our rainy seasons, however, do not consist of deluges of rain that overflood the country, but of daily showers, occurring in the early part of the afternoon, lasting an hour or two, leaving the sky bright and clear, the air cool for the rest of the twenty-four hours, comfortable to man, and favorable to luxuriant vegetable growth. The rainy seasons, when regular, continue day after day, for about sixty days, but often there is an interval of clear, sunshiny weather, for about a fortnight, between the rainy periods, which carries the rainy season into the fall months. Upon examination of the tree, it will be found that, when those severe droughts have put a stop to vegetable growth, a concentric ring well defined has been produced, and the growth which has occurred during the rainy season and until winter's cold has formed another and perhaps a thicker ring, making two rings in one year. But the phenomena of such a year are not necessarily repeated each year, for considerable variation occurs.

What physiological meaning is attached to these rings? They simply mark the amount of growth of woody matter deposited day by day between the periods when a stop to vegetable growth has prevented daily deposit and produced a line of demarkation, whether from drought of summer or cold of winter.

For some two or three years before his lamented death, Professor Jeffries Wyman was exploring the mounds of Florida. It was my privilege to enjoy his acquaintance and learn his views on matters of science in which we were both interested. I have heard him express his belief that he had reached an approximate age of some of the mounds which he had explored, by the indications which the trees growing upon them had furnished. It so happened that we were one time walking down-town together and passed a lot where preparations for building a dwelling-house were going on, and a tree which stood upon the proposed site was being cut down. He remarked that it was sacrilege to cut down so noble a tree; he would have changed the site of the house and let the tree remain as a shade, "for," said he, "it would take a hundred years to produce such another tree." In that, I told him, he was mistaken, as I knew the age of that tree, and it was not yet thirty years old. "Impos-