Page:Popular Science Monthly Volume 27.djvu/446

430 and begin to bear in about five or six years, yielding then from twenty to thirty oranges each, and increasing their crop for ten years till in full bearing, when they produce from two to three hundred, and, in most favorable circumstances, one thousand oranges a year. The trees remain fruitful for more than thirty years. The cost of cultivating and attending a thousand orange-trees in Brazil is estimated at about seventy dollars a year.

Climate and Vegetation.—In a paper on the relations of climate and vegetation, M. M. Bergsman, of Flushing, reaches the conclusion that a mixed climate, with relatively mild winters and warm, sunny summers, is the best suited for the vegetation of the temperate zone. Corn can be cultivated only as a green vegetable in England; is profitable in Western Europe only to 46°, and in the valley of the Rhine to 49°, but in certain regions of North America to 51, and even under the Polar Circle in Norway, where it has the sun day and night. Plants much resembling those of Central Europe grow in the Amour region of Siberia, where precipitation occurs only in summer, and that season is warm, in the face of a winter temperature much lower than is observed in the most northern parts of Lapland. Radishes, turnips, rape, and the potato grow as far north as there are settlements, but in the extreme north the potatoes are only as large as walnuts, and the plant never blossoms in Greenland. When comparing extreme continental climates with extreme sea climates, the continental climate has the advantage. The extreme southern limit of phanerogamous plants is in the South Shetland Islands, latitude 60° to 63° south, and the last trace of vegetation, in cryptogams, is found on Cockburn Island, 64° south. At the same latitude in Northern Siberia is a forest of very high coniferous trees. The chief reason that corn can not be cultivated in Siberia beyond 62°, at Yakutsk, is on account of the constantly frozen condition of the ground at a short distance beneath the surface. In Europe, even, the climate of the northern parts of the British Isles is not suited for many vegetables and other cultivated plants. It is in Germany where almost all the plants of the temperate zone and those commonly cultivated can be found. Even in that country the summer temperature in general is only a few degrees above that calculated for the latitude. Germany is crossed in July by the isotherm of 68°, and Britain by that of 59°, but the difference in vegetation is not caused by the difference of 9° in mean temperature, but by the difference in the amount of sunshine.

Denudation of the Continents.—Mr. T. Mellaid Reade, addressing the Liverpool Geological Society on "The Denudation of the Two Americas," showed that one hundred and fifty million tons of matter in solution are annually poured into the Gulf of Mexico by the Mississippi River. This, it was estimated, would reduce the time for the denudation of one foot of land over the whole basin—which time has hitherto been calculated solely from the matter in suspension—from six thousand years to four thousand years. Similar calculations were applied to the La Plata, the Amazon, and the St. Lawrence; and Mr. Reade arrived at the result that an average of one hundred tons per square mile per annum is removed from the whole American Continent. This agrees with results he had previously arrived at for Europe, from which it was inferred that the whole of the land draining into the Atlantic Ocean from America, Africa, Europe, and Asia contributes matter in solution which, if reduced to rock at two tons to the cubic yard, would equal one cubic mile every six years.

Photographing Colors.—Professor H. W. Vogel has made a report of the final results of his researches on the means of photographing colored objects in their natural shades. Sensitive plates are affected only by the more refrangible rays, so that they present totally unnatural and distorted pictures, as to the shading, of colored objects. Believing that the sensitive collodion is affected only by such colors as are absorbed by it, Professor Vogel's efforts have been directed to making his plates sensitive to less refrangible rays by alloying the silver coating with a substance capable of absorbing those rays. His experiment succeeded with the natural colors, but he could not obtain an effect with the duller artificial colors. He then sought for organic substances