476 



BIOLOGY AND HUMAN LIFE 



twisting of the parts of the pod, as in the touch-me-not and the 

 lupine (see Fig. 197). 



Most plants depend upon outside agencies to scatter their 

 seeds for them. The wind is active in the case of species whose 

 seeds are either very small and light (the orchids) or supplied 

 with expansions in the form of wings or tufts of hair that 

 furnish a large area of contact with the air (see Fig. 196). 





W 



Fig. 198. Fruits scattered by passing animals 



I, beggar-ticks, or bur marigold (Bidcus jrondosa); 2, burdock (Lappula eckinata); 

 3, small-flowered agrimony (Agrimouia parviflora); 4, carrot (Daucus carota); 

 5, enchanter's nightshade (Circaea lutetiana); 6, cocklebur {Xanthium canadensis); 

 7, bur grass {Cenchrus tribidoides); 8, spike rush (Eleocharis ovata). (i, 4, 8, 



enlarged; 2, 6, reduced) 



Fruits that have hooks, as the cocklebur and beggar-ticks, 

 attach themselves to the fur of passing animals and are carried 

 considerable distances from the parent plant (see Fig. 198). 

 Seeds that are inclosed in edible fruits are often distributed by 

 animals, as they are swallowed and are then discharged from 

 the intestines without having suffered any injury. Cherries, 

 blackberries, and other small fruits are commonly distributed 

 by blackbirds, robins, thrushes, and other birds (see Fig. 199). 



