76 GRASSES OF IOWA. 



Several species of Aveua, A. barbatum and A. fatua, our wild 

 oats, are similarly provided with twisted awns that help to 

 bury the seed. Several species of Aristida also bury them- 

 selves, as do members of the genus Danthonia. In Iriticum 

 ovatum the entire spike falls off. It possesses a very pointed 

 base, and the numerous rough awns pointed outward, thereby 

 movements of the wind exart a pressure upon the point which 

 drives it into the ground. 



The peculiar use of the awns of Arena sferilis are described 

 by Hackel as follows: " Two strongly awned fruit-bracts fall 

 off, fastened together; in moist surroundings the twisted awns 

 begin to rotate their diverging upper halves, consequently ihey 

 cross and press against each other until the bracts are forcibly 

 separated, thus giving the fruit au impetus which throws it 

 off for some distance. 



In many cases seeds of grasses are distributed by birds and 

 animals wh'ch feed upon them but do not digest them. Birds 

 of various kinds freely feed upon Setaria glauca, S. viridis, Pan- 

 icum miliaceum, often carrying them great distances. Many 

 herbivorous animals also help to carry seeds in this way, as is 

 evidenced by seeds of many grasses that come up from excreta. 

 This manner of distribution for most seeds is a most precari- 

 ous one, as the ' ' seeds ' ' pass through the digestive canal, 

 germination is hastened, and thus they may be destroyed. 

 But the fleshy berries of many Bambusese are especially 

 adapted to animals which do not destroy or digest the seeds. 

 Many animals, especially wading birds and others, carry seed 

 of grasses in the mud that clings to their feet. 



The light specific gravHy of many grass fruits make them 

 especially susceptible to dissemination by water. The chaff, 

 in many cases, remains persistent, and so constructed that the 

 whole floats readily. Thus rice and wild rice will float for a 

 time until they are soaked with water. Water, however, adds 

 mostly in a mechanical way, currents of water carrying away 

 large quantities of earth with which are mixed seeds of grasses. 

 Neighboring farms have frequently been sown with seeds of 

 wild oats in this way, as has been witnessed in man}^ cases 

 along the bluffs of the Mississippi in Wisconsin and Minnesota. 



Certain fruits of grasses are thrown out by expulsion. Pro- 

 fessor Beal says of Sporobolus: " The ovary of Sporobolus is 

 very thin and tender. Free seeds may often be seen still 

 adhering to various portions of the glumes and branches of the 



