DISPERSAL AND GERMINATION OF SEEDS 173 



dispersal brought about by oceanic currents, both by waves 

 carrying seeds along the coast, and also by the deeper cur- 

 rents that extend from continent to continent or to oceanic 

 islands. It has been found that many seeds can endure even 

 prolonged soaking in sea-water and then germinate. From 

 a series of experiments, Darwin estimated that the seeds of at 

 least fourteen per cent of the British plants can retain their 

 vitality in sea-water for twenty-eight 

 days. At the ordinary 

 rate of oceanic currents, 

 this period would per- 

 mit seeds to be trans- 

 ported over a thousand 

 miles. 



The dispersal of seeds 

 by means of animals is 

 a very common method, 

 but it is accomplished 

 in so many ways that 

 only a very few illus- 

 trations can be given. 

 Water birds are great 

 carriers of seeds, which 

 are contained in the 

 mud clinging to their 

 feet and legs. This mud from the borders of ponds is 

 usually filled with seeds of various plants. Water birds 

 are generally high and strong fliers, and the seeds may 

 be transported in this way to the margins of distant ponds 

 and lakes, and so become very widely dispersed. In many 

 cases, seeds or fruits develop grappling appendages of various 

 kinds, forming the various " burs " that lay hold of animals 

 brushing past, and so the seeds become dispersed. Common 

 illustrations of fruits with grappling appendages are Spanish 

 needles (Fig. 142), beggar-ticks (Fig. 143), stickseeds, etc.; 



FIG. 142. Fruit 

 (akene) of Spanish 

 needles with barbed 

 appendages. 

 After KEENER. 



FIG. 143. Fruit of beg- 

 gar-ticks with barbed 

 appendages. After 

 BEAL. 



