INTRODUCTION. XIU 



of sea-weed; like little branches of the fir-trees 



which bear the pistachio nuts, that we believed the 



ships would run aground for want of water." They 



supposed, as is usually the case, that the presence 



of vegetation denoted the existence of shallows — 



" For where the waves are shining red, 



And the russet sea-leaves glow, 

 Mariners with prudent dread 

 Shun the shelving rocks helow." 



Various opinions have been held respecting the 

 origin of this floating vegetation. No species of 

 Sargassum, exactly similar to it, has been found 

 growing on any coast, though numerous examples 

 of the genus are common on the shores of tropical 

 countries. According to the united testimony of 

 botanists who have examined this plant, no roots 

 have ever been detected, and as it but rarely pro- 

 duces fruit, it would appear to be propagated by the 

 accidental fracture of the old frond, which is very 

 brittle — the detached portion shoots out afresh, and 

 forms a new plant ; affording a vegetable parallel 

 to the fresh water Hydra amongst animals, several 

 portions of which will, after the lapse of a short 



