Read it through once

It is, however, in the exquisite modifications of those fruits which are blown by the wind that we find the most beautiful contrivances of all. They are effective also. Seeds are often so small as to be like dust particles, and such may be carried in the air to almost incredible distances. That of _Goodyera repens_ weighs only 1/200,000,000 of a pound, that of _Monotropa_, ·000,000,006 lb. It is no doubt by the wind that the spores of lichens are carried from one mountain to another. On a map of the world the distance from the Arctic to the Antarctic, between the North and South Poles, seems enormous. Moreover, the amount of water, desert, tropical forest, and cultivated land in this extent of country is very great. There are but few rocks on which lichens could manage to grow. And yet of the Antarctic Lichens in the South Polar regions, and which are also European species, more than 73 per cent. are found in the Arctic or North Polar regions.[116]