NATURAL HISTORY. 195 



the boundaries of the torrid zone, their appearance 

 serves to indicate to mariners the vicinity of the 

 tropic, whence their common name of tropic-birds. 

 On land, where they seldom resort, except to feed, 

 they perch upon trees. They are closely related by 

 affinity to the gannets. The occasional visitants are 

 very numerous, many of them accidental and of great 

 interest. 



Eminently characteristic of a tropical shore is the 

 dense belt of mangrove-bushes which lines a bay 

 at Somerset, termed Long Bay. To a European, it 

 is a strange sight to see a grove of trees growing 

 actually out of the sea ; and his admiration is not 

 diminished when he examines more closely the struc- 

 ture of these singular plants. The trunk of every 

 tree springs from the union of a number of slender 

 arches, each forming the quadrant of a circle, 

 whose extremities penetrate into the mud. These 

 are the roots of the tree, which always shoot out 

 in this arched form, often taking a regular curve of 

 six feet in length before they dip into the mud. 

 The larger ones send out side-shoots, which take 

 the same curved form at right angles ; and thus, 

 by the crossing of the roots of neighbouring trees, 

 and of the subordinate roots of each, a complex 

 array of arches is produced, on which one may 



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