GRASSES OP IOWA. 



73 



and is either bodily carried up in the air or rolls along the 

 ground. Many of our native grasses like Eragrostis are carried 

 in a similar way. To be sure, many of the seeds fall long 

 before they sejjarate from the plant. And yet dozens of fruits 

 may be counted on a single panicle. The wind may also carry 

 the seed over the snow during win'er. 



Animals and hygroscopic movements. — Animals are most effi- 

 cient in conveying the seed of many grasses. The stiff, sharp 

 spines of the involucre in Sand Bur {Genchrus tribuloides) are 

 most efficient in piercing the skins of animals. Indeed it 

 sometimes causes considerable annoyance to animals and man. 

 In Streptochaeta, says Hackel, "The ripe fruit hangs from 

 delicate spiral threads (the awns) which are fastened together 

 at the end of the spike; they are free below, and their soft- 

 pointed bracts, bent outward, act like fish-hooks by catching 

 into the fur of any animal that touches them in passing." 



Our common Squirrel-tail grass {Hordeum jubatum) is most 

 efficiently carried by animals. The.spikes, when mature, break 

 up into joints, and although the joints are not sharp-pointed 

 they readily cling to the fleeces of animals. So, too, do the 

 broken points of Sitanion cling to animals. 

 4 3 



12 5 



Fig. 50. 1, Foxtail (Setaria vlridw); ?, Setaria glaum; 3, Setaria vcrtieillata. The seeds 

 of all three species carried by animals, especially sheep and cattle. 4, Panicum. san- 

 guiiiale; 3, P. cnis-galli. The seeds of these are carried by birds, used as food. 



