310 ANNUAL REPOET SMITHSONIAN INSTITUTION, 193 4 



DISPERSAL BY ANIMALS 



Many grasses are adapted to dispersal by animals (including 

 man). The seeds of this class have a covering or appendage which 

 sticks to the wool, hair, or fur of animals, or to the clothing of man. 

 The familiar sandbur has barbed spines for the purpose of attach- 

 ment. Needlegrasses {Stipa) and three-awns (JL/v's^/t/tf) have seeds 

 with sharp, barbed points that penetrate wool or clothing. The base 

 of the spikelets of Bromus rigidus (called ripgut grass by stockmen) 

 is sharp and barbed. The seeds penetrate wool and, much worse, get 

 into the eyes and nostrils of grazing animals, causing serious injury 

 to stock in western States where the grass is often abundant. 



DISPERSAL OVER TRADE ROUTES 



The methods of dispersal described above account for the spread 

 of species in rather restricted areas. We find, however, that certain 

 kinds of plants, known as weeds, travel widely over the earth. The 

 spread of such plants has been greatly expedited during the last 

 few hundred years. The more rapid rate of travel coincides with 

 the development of the means of transportation by man. Many 

 plants, grasses among them, have been carried along the channels 

 of trade through the agency of man. Some seeds have been carried 

 entirely by accident; others have been carried as impurities in agri- 

 cultural seed, accidentally, to be sure, but as a part of a direct inten- 

 tion. 



Bluegrass {Poa pratensis) is not a native of the United States 

 but is now so widespread that, did we not know its histoiy, it would 

 be assumed to be native. From time to time noxious weeds have 

 suddenly appeared in interior States, brought in along with im- 

 ported seed of alfalfa, cereals, or meadow grasses. When such 

 chance introductions have found favorable conditions for their 

 growth, they have spread and not infrequently have become a menace 

 to crop plants. 



USES OF GRASSES 



From the standpoint of mankind the primary uses of grasses are 

 as food for man and feed, fodder, or grazing for domestic animals. 



The grasses furnishing food for man are the cereals, the most 

 important of which are wheat, corn (maize), rice, barley, rye, and 

 oats. In earlier days other grasses were used, such as millet {Seta- 

 Tia), Sorghum, African millet (Eleusine), broomcorn millet {Pani- 

 cum 7niliaceum), Japanese millet (Echinochloa) , pearl millet 

 {Pennisetwn) , teff {Eragrostis ahyssinica), certain of the wheat 

 genus (emmer, einkorn, and spelt), forerunners of our modern cul- 

 tivated forms, and other less familiar grasses. Many of these food 



