. Biology in America. Biology. Geographical Distribution 161 are well nigh as varied as are those of human society. Tem- perature, moisture, wind and light are the four principal parts of the plant's environment, but these in turn are de- pendent on other factors, such as altitude, topography and soil. The structure of the plant itself determines its re- sponse to these factors and its survival or extinction, while the relation of plant to plant in determining such factors as light, food supply, growing space, etc., and the inter- relationship between plants and animals, affecting transport of
. Biology in America. Biology. Geographical Distribution 161 are well nigh as varied as are those of human society. Tem- perature, moisture, wind and light are the four principal parts of the plant's environment, but these in turn are de- pendent on other factors, such as altitude, topography and soil. The structure of the plant itself determines its re- sponse to these factors and its survival or extinction, while the relation of plant to plant in determining such factors as light, food supply, growing space, etc., and the inter- relationship between plants and animals, affecting transport of seeds, and forage for herbivorous animals, all have a life and death meaning in the existence of the plant. Not only is the distribution of plants determined in large measure by that of animals, but even more is the occurrence of the latter dependent upon that of the former. Especially /so I2a 30 iO JO /?«? ISO 160. Diagram of the Six Great Zoogeographical Eealms of the Earth After Sclater and Wallace. is this tiiie of herbivorous types, which necessarily are de- pendent upon the presence of their forage plants. The move- ments of grazing animals, such as horses and cattle, are in particular dependent upon the abundance of grasses, and in the early days of the West, Indians and white men alike guided their movements in the search for buffalo largely by the condition of the prairies over which the bison roamed. Not only are the herbivorous types dependent on the vege- tation in their movements, but also the carnivorous animals which prey upon the former. In the northern forests the movements of the deer in winter largely determine those of their enemy, the wolf. During the mouse plague in the Hum- boldt Valley in Nevada in 1907-8 the abundance of the mice attracted thither large numbers of hawks to feed upon them. Based on the distribution of their animal inhabitants the. Please note that these images are extracted from scanned page images that may have been digitally enhanced
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