Page:Popular Science Monthly Volume 29.djvu/371

Rh from the shores of the Arctic Ocean to the coasts of Bolivia, were everywhere largely the same; always enough of identical species to show that arctic and tropical environments were essentially alike. It seems, if possible, still more incredible that in later times—say, in the Miocene—species which originated in Spitzbergen and upper Greenland could migrate to low latitudes, and still show no change in specific characters.

It certainly was to be expected that conditions so unlike—I refer, now, only to the long days and nights—should have been attended by widely diverse plant-life.

The belief that such would have been the case is strengthened by the fact noticed by Mr. H. C. Watson, and quoted approvingly by Mr. Darwin in his "Origin of Species," that, "in receding from polar toward equatorial latitudes, the Alpine or mountain floras really become less and less arctic."

But, were they truly arctic, and identical with those now in Spitzbergen, such floras, accustomed to a hibernation of nine months, might well be indifferent as to where that time was spent, whether in the cold and continuous darkness of an arctic night, or in the cold of a winter on a low-latitude mountain-top. On the other hand, the plants, e. g., of the Carboniferous, were not arctic plants, but were warm-temperate, if not tropical, and there was no arctic cold, but "a warm, moist, equable atmosphere," in which they "flourished luxuriantly." Another corroborative fact is found in the peculiar structure of certain post-glacial arctic trees. A conifer, found standing in latitude 72°, and of post-glacial origin, was brought to England by Sir E. Belcher, where Sir William Hooker made a microscopical examination of its structure. He found that it differed remarkably from any other conifer with which he was acquainted. Each annual ring consisted of two zones of tissue: the inner zone was narrow, of a dark color, formed of more slender, woody fibers, with few or no disks upon them; the outer zone was broader, of a pale color, and consisted of ordinary tubes of fiber of wood marked with disks such as are common to all coniferæ. These characters he found in all parts of the wood. They suggest, as he says, the annual recurrence of some special cause that modified the first and last formed fibers of each year's deposit, and this cause, he thinks, is found in the peculiar conditions of an arctic climate, where the days were at first very short, a few hours only of sunshine. Then the first and imperfectly developed fibers were formed. As the days grew longer and longer, and the solar rays at last became continuous, the woody fibers became more perfect, and were studded with disks of a more highly organized structure than are usual in the natural order to which this tree belongs.

Since Spitzbergen is nearly 5° farther north, such or similar effects ought to show themselves there in greater intensity in the conifers of