Broad Fronts Research Articles

Twenty years of physics: Acoustics

THE SCIENCE OF ACOUSTICS touches on practically every aspect of human experience; hence it advances on broad fronts ranging all the way from basic physics and chemistry through most branches of engineering to the life sciences. The extent of its development during the past two decades may in some measure be gauged by the growth in membership of the Acoustical Society of America from 1300 in 1947 to 4150 in 1967. During the same period the number of pages published per year in the Society's Journal grew from less than 1000 in 1947 to 4150 in 1967. This is typical of the world progress in acoustics.

A Note on Unusual Plants in the Flora of Northwestern Nebraska

During the past twenty years several unusual, local floras have been described in Canada and the Great Lakes Region (Raup 1941, Fernald 1935). Significant floras remain to be studied in more detail than has been done to this time in regions west of the Mississippi River along broad fronts ahead of the several lobes of glacial deposits and in areas which have escaped glaciation. The flora of the non-glaciated region of the Mississippi Valley in southeastern Minnesota and adjacent areas in Iowa and Wisconsin is of special interest, but plants in localities on both the west and east edge of the Des Moines Lobe of late Wisconsin glaciation in northwestern and northeastern Iowa are of equal interest (Cooper 1935, Hay den 1940). The flora of the Black Hills is also important because many eastern and northern plants are here on the western or southern border of their range (Mclntosh 1931). The same is true of a large number of rare plants of northern Nebraska, especially in the sand hills, in the Niobrara Valley, and in the canyons of Pine Ridge. Dodecatheon amethystinum, described by Fassett (1931), is an example of a rare plant confined to a limited area. It occurs occasionally on the limestone cliffs of the non-glaciated region. Most of the interesting plants, however, are merely outlyers or samples of discontinuous distribution. A study of Rubus odoratus and R. parvifiorus by Fassett (1941) exemplifies this type of distribution. A part of Fassett's study compares outlyers of Rubus parvifiorus in the Great Lakes Region with specimens from the Rocky Mountains and the Pacific Coast where the greatest development of this species has taken place. A large number of unusual plants of Northern Nebraska is of similar nature. These are mesophytic species, which are now widely separated from their major distribution and occur in a semiarid region because many mesophytic habitats result from the interrelations of local geology, soils, topography, and ground water. Many of the rare plants were recorded in Nebraska during the years of exploration by Bessey (1898), Rydberg (1895), Bates (1914), and Pool (1913). No full summary, however, has been made of the flora from any special locality, and the nature of the environments which permitted survival of mesophytic plants has not been recorded fully. The history of these unusual communities in light of new information concerning the Pleistocene Geology of Nebraska and adjacent states is reserved as a part of another paper.