204 



GROWTH AND WORK OF PLANTS 



seeds of many coastal plants are distributed to great distances by 

 the ocean currents. It has been found that many seeds will 



retain their vitality after immer- 

 sion in the salt water cf the 

 ocean for three or four weeks, 

 and some will germinate after 

 prolonged immersion. Darwin 

 has shown by experiment that 

 about fourteen per cent of the 

 seeds cf British plants will bear 

 immersion in sea water for four 

 weeks and still germinate. The 

 distribution of certain plants en 

 near-by islands, or in some 

 cases on islands quite remote, 

 is sometimes explained by the 

 ability of the seeds to bear the 

 prolonged soaking of an ocean 

 Flg- l66- voyage from one shore to 



Seed pod of tick trefoil (Desmodium); at ' e 

 the right some of the hooks greatly magnified, another. 



Fig. 167. 

 Seeds of Geum showing the hooklets where the end of the style is kneed. 



