MARINE BOTANY. 99 



physical force. The waves may tear from the Coral-reef 

 thousands of blocks ; but what does this signify against the 

 piled-up labours of countless myriads of little architects, 

 who are engaged day and night in extracting calcareous 

 atoms from the foaming waves, and arranging them in 

 systematical constructions ? Thus we see the vital strength 

 that exists in the soft gelatinous body of a Polype conquer- 

 ing the gigantic power of an Ocean, which neither the 

 works of human skill nor those of inanimate nature can 

 withstand. 



The Reef-forming Corallines, which is this way defy the 

 utmost efforts of the waves, are, in other respects, extremely 

 delicate and sensitive. They require a warmish water for 

 existence, and only inhabit those seas whose temperature 

 never sinks below 60°. 



The effect of the ocean-currents has, consequently, a 

 great influence on their appearance. At the Gallipagos, 

 which lie below the Equator, but are exposed to the chilling 

 influence of the Peruvian Stream, no Corals are found ; 

 while, favoured by the warm Gulph Stream, they are seen 

 round the Bermudas, although these islands lie from four to 

 five degrees beyond the usual boundaries of the Coral reef. 



A clear unpolluted saline water is also indispensably 

 necessary for their existence. They shun slimy, sandy 

 coasts ; and opposite flowing rivers there are corresponding 

 holes in the reefs they throw up. 



There are also many unexplained circumstances which, in 

 some parts of the sea, favour the congregation of building 

 Polypodoms, and in others compel their entire absence. 

 Why, for instance, the north-western coast of Africa, St. 

 Helena, Ascension, San Fernando, the Cape Yerde islands, 

 where the temperature is most suitable, are entirely free 

 from Corals, which are found so frequently on the eastern 

 coasts of Zanzibar and in the adjacent seas, no one can 

 satisfactorily explain. As the sea is frequently fathomless 

 at a short distance from the Coral-reef — as off the Keeling 



