134 DISSEMINATION OF SEEDS. 



DISSEMINATION FAVORED BY THE PLACE OF GERMINATION. 



By a peculiar provision of nature, the increase in the 

 number of mangrove trees is insured. The seeds of 

 the mangrove germinate before leaving the fruit. The 

 long, thick radicle pierces through the testa and the peri- 

 carp, and the young plant rapidly grows downward until 

 the fruit falls off when the roots penetrate the mud. 

 After this the plant rapidly increases until it becomes a 

 large tree. 



DISSEMINATION OF SEEDS BY MOUNTAIN STREAMS. 



A mountain stream or torrent frequently Avashes down 

 to the valley seeds which have accidentally fallen into it, 

 or which the water has swept from the banks as it has 

 overflowed them. These, as one stream unites with 

 another until a broad river is formed, are carried by it 

 to remote localities sometimes to the mouth, and there, 

 if they are dropped upon a soil suited to their growth, 

 the seeds spring into life and cause a growth of plants 

 unlike those in the vicinity. Thus the shores of the 

 Baltic are visited by seeds from the interior of Germany ; 

 the shores of the Gulf of Mexico, by seeds from the 

 northern and western parts of the United States. 



DISSEMINATION BY RIVER-RAFTS. 



In large rivers there is often found a formation called 

 a river-raft ; it consists of pieces of logs and timber fas- 

 tened together by various substances which they have 

 collected in their journey from the source of the river. 

 These constantly increase in size and sometimes form a 

 natural bridge across the river. Sometimes in the debris, 



