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Page:Popular Science Monthly Volume 34.djvu/730

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THE POPULAR SCIENCE MONTHLY.

side of their bases of support, which protect them from the intrusion of the heavier particles. For that reason perpendicular and water-logged or floating timbers, submerged stumps of trees, and branches drooping into the water from trees or bushes along the banks, are favorite locations. They do not disdain more temporary support, such as weeds and water-grasses. . . . Through the clear water of our Northern lakes we may often see them lying in slender lines upon the leaves of submerged weeds, or in beautiful, cushion-like masses upon the stones or gravel." The best season for collecting them is from July till late in November.

 

Geological Floras.—M. de Saporta's views on the origin of our forest-groupings were substantially concurred in by Prof. W. Boyd Dawkins, in his vice-presidential address before the Geological Section of the British Association. Having referred to the characteristic features of the earlier floras, much as M. de Saporta has done, and to the antiquity of the gingko (which has descended from the Carboniferous age), he says: "In North America the flora of the Dakota series so closely resembles the Miocene of Switzerland that Dr. Heer had no hesitation in assigning it in the first instance to the Miocene age. It consists of about one hundred species, of which about one half are closely allied to those now living in the forests of North America—sassafras, tulip, plane, willow, oak, poplar, maple, birch, together with sequoia, the ancestor of the giant redwood of California. The first palms appear also in both continents at this place in the geological record. In the Tertiary period there is an unbroken sequence in the floras, as Mr. Starkie Gairdner has proved, when they are traced over many latitudes, and most of the types still survive at the present day, but slightly altered. If, however. Tertiary floras of different ages are met with in one area, considerable differences are to be seen, due to progressive alterations in the climate and altered distribution of the land. As the temperature of the northern hemisphere became lowered, the tropical forests were pushed nearer and nearer to the equator, and were replaced by plants of colder habits from the northern regions, until, in the Pleistocene age, the arctic plants were forced far to the south of their present habitat. In consequence of this, Mr. Gairdner concludes that ' it is useless to seek in the arctic regions for Eocene floras as we know them in our latitudes, for during the Tertiary period the climatic condition of the earth did not permit their growth there. Arctic fossil floras of temperate and, therefore, Miocene aspect are in all probability of Eocene age, and what has been recognized in them as a newer or Miocene facies is due to their having been first studied in Europe in latitudes which only became fit for them in Miocene times. When stratigraphical evidence is absent or inconclusive, this unexpected persistence of plant-types or species throughout the Tertiaries should be remembered, and the degrees of latitude in which they are found should be well considered before conclusions are published respecting their relative age.' This view is consistent with that held by the leaders in botany—Hooker, Dyer, Saporta, Dawson, and Asa Gray—that the north polar region is the center of dispersal, from which the dicotyledons spread over the northern hemisphere."

 

Science and Trade-Routes.—In the first part of his presidential address before the Geographical Section of the British Association, Colonel Sir C. W. Wilson showed, by numerous historical references, how the trade routes of the world are and have always been governed by physiographical conditions, and by accidents of war and human operations, which, making one route inconvenient, have compelled the opening of another. To cope with these conditions, and find and possess the best route, is one of the functions of the scientific geographer. The discovery of the Cape route was no mere accident, but the result of scientific training, deep study, careful preparation, and indomitable perseverance. Prince Henry, having determined to find a direct route to India, invited the most eminent men of science to instruct a number of young men who were educated under his own eye, and in a few years he made the Portuguese the most scientific navigators ia Europe. The voyage of Vasco da Gama, with its grand commercial results, followed. For a correct determination of the lines which the shortened trade-routes and great maritime canals we are seeking to locate should