Fourth Series, Bulletin Volume 16

Fourth Series, Bulletin Volume 16

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 edition. Excerpt: ...of northwestern and eastern outlets to the postglacial waters retarded the northern dispersal of many land species. The conditions favored for a long time the extension of aquatic vegetation only, and the development of marginal associations. The more elevated, drier portions afforded restricted areas in which the occasional seeds brought by wind and birds established themselves, while in the undrained and poorly drained depressions the establishment of the bog plants took place. As in the case of the tundra vegetation, physiographic conditions rather than mineral soil preferences determined their habitat. Slowly they worked themselves up the valleys along the dendritic tributaries in diverging directions nearer to the divide. The tundra vegetation was closely followed by them and perished wherever the vegetation of the sub-arctic transition zone became-firmly entrenched. The long duration of the conditions immediately following glacial times, the massive beach ridges, bars, cut-off ponds and innumerable lakes furnished a variety of habitats for these plants, much more extensive than that at present; they were favorable to a rapid dispersion and repopulation. The genetically related associations were not isolated from one another by any considerable space, but occupied the region more continuously than found today. They were gradually reduced in extent through natural causes. The arctic vegetation aspect did not remain fixed but moved, and increased or decreased in extent depending upon physiographic and climatic changes. Constantly the tone of the landscape changed. The lines of movement northward radiated in all directions. From the banks of the great local streams and lakes, from the more temperate regions, and from the southern centers of...
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Product details

  • Paperback | 192 pages
  • 189 x 246 x 10mm | 354g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236597966
  • 9781236597960