Desert Botanical Laboratory of the Carnegie Institution Volume 6

Download or read book Desert Botanical Laboratory of the Carnegie Institution Volume 6 written by Frederick Vernon Coville and published by Rarebooksclub.com. This book was released on 2013-09 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 edition. Excerpt: ...are characterized by a lack of running streams, or of a permanent run-off, although in some instances these districts may be traversed by large rivers which have their sources in distant mountain ranges as in the case of the Nile in Africa and of the Colorado river in America. The rainfall in a desert may be so heavy at certain seasons as to produce torrents of great volume, which rushing downward over the slopes and mountain sides, wear distinct streamways extending out into the plains below in some instances for miles; but the flow soon ceases after the rains have passed and the stream beds become dusty channels until the next rainy season. Striking examples of such streamways are to be seen in the great Sonoran desert in northwestern Mexico. It is evident that districts in which the average rainfall is not much greater than the evaporation are in a very critical condition, since in seasons of minimum precipitation the amount of water received may be less than that lost, and drought may result, often with direful effects on agricultural operations and economic conditions in general. The seasonal distribution of the rainfall is a matter of importance in regions where evaporation is nearly as great as precipitation. If the rainfall occurs within a brief period the remainder of the year must be extremely dry and the region will show distinct desert conditions with a tendency on the part of the native plants to develop marked storage capacity for water. The distribution of the scanty rainfall throughout the year in any region will favor the development of slowly growing xerophytic forms. These factors are further considered on page 28. Arid deserts occur in all of the great land divisions and reach an enormous extent in Africa, Asia, and...