132 THE WORLDS LUMBER ROOM. 



at once close their flowers. Yet a twig of coral may be 

 broken off without being killed ; in two or three hours it 

 will recover sufficiently to open out again, and if placed 

 in a suitable position will soon begin to sprout and grow 

 after the family pattern. 



It has not at present been possible to calculate the rate 

 of growth with much certainty, but twenty corals planted on 

 a sand-bank east of Madagascar, grew nearly three feet in 

 height and several feet in length in the course of six or seven 

 months ; and the copper sheathing of a vessel which had 

 spent twenty months in the Persian Gulf, was covered with 

 a hard crust of coral two feet in thickness. No doubt, how- 

 ever, the rate of growth varies in different species. 



Most of the Bermuda corals resemble anemones or 

 groups of anemones, the stony skeleton being entirely con- 

 cealed ; but in a few, as the brain-coral, which grows in the 

 shape of large domes, it is only just coated with a film of 

 yellow or greyish living matter. 



Like the bog-mosses, many of the coral-polyps go on 

 growing above while they die below, and thus the large solid 

 domes of Astrsea are quite dead within, the living portion 

 being confined to the surface and only half an inch thick, or 

 even less. 



The great masses of coral rock, called reefs, which in 

 some places extend for hundreds of miles along the coast 

 and form natural breakwaters, are composed only in part of 

 living coral, and consist chiefly of the consolidated debris 

 of many kinds of coral and corallines, the shells of mollusks, 

 and the tubes of many sea-worms. 



The great reef on the N.E. of Australia is 1,200 miles 



