SEED DISPERSAL 



203 



akenes of the same genus are called " Spanish needles." The 

 oval fruit of the " cockle-bur " is covered with long hooks. 

 In the " burdock " the numerous bracts, surrounding the head 

 containing the numerous akenes, are extended into a long 

 slender process terminating in a hook. The " sticktights," or 

 " tick trefoil," are sections of the pod of a leguminous plant (Des- 

 modium = Meibomia) which are covered with numerous hooks. 

 In the various species of avens (Geum) the long style of the akene 

 is jointed near the end and curved into a hook. It separates at 

 the joint, leaving the hook on the long beak (fig. 167). Besides 

 the seeds provided with 

 grapplers many seeds ad- 

 here with mud to the feet 

 of animals, and in the case 

 of birds are often trans- 

 ported to great distances, 

 especially by wading birds 

 and waterfowl. 



340. Dispersal of seeds 

 by water. Streams have 

 long been recognized as 

 lines for the transport and 

 centers of distribution of 

 seeds. Some seeds because 

 of their light weight and 

 slightly impervious coats 

 float for long distances on 

 j the water. Others which 

 may sink are swept along 

 in the strong current. 

 Even on high ground, 

 many seeds are carried to 

 considerable distances by 



the " run-off " water during heavy rains. Seeds are distributed also 

 along the shores of ponds and lakes as they float on the water 

 which is moved by winds. Also along the shores of the ocean the 



t ; ig- 165. 

 Fruits of tick trefoil (Desmodium). 



