STRUCTURE AND GROWTH OF ZOOPHYTES. 53 



evident that if the land supporting the growing coral were very 

 gradually sinking, the upward increase of the coral might still 

 be without limit. 



There is hence sufficient means provided for the production of 

 coral material for islands, however numerous. These humble 

 ministers of creative power might, without other attributes than 

 those they now possess, have laid the foundations of conti- 

 nents, and covered them with mountain ranges. This remark 

 requires no limitation if we allow the requisite time, and connect 

 with the power of growth such other agencies, soon to be ex- 

 plained, as have been at work in the Pacific since the reefs were 

 there in progress. 



The death of the polyps about the base of a coral tree would 

 expose it seemingly to immediate wear from the waters around 

 it, and especially as the texture is usually porous. But nature is 

 not without an expedient to prevent a catastrophe that would be 

 destructive to a large part of growing zoophytes, and would pre- 

 vent the indefinite increase just explained. The dead surface be- 

 comes the resting-place of numberless small incrusting species of 

 corals, besides Nullipores, Serpulas, and some molluscs. In many 

 instances the lichen-like Nullipore grows at the same rate with 

 the rate of death in the zoophyte, and keeps itself up to the 

 very limit of the living part. The dead trunk of the forest be- 

 comes covered with lichens and fungi, or in tropical climes, with 

 other foliage and various foreign flowers : so among the coral 

 productions of the sea, there are forms of life which replace the 

 dying polyp. The process of wear is thus entirely prevented. 



The older polyps, before death, often increase their coral secre- 

 tions within, filling the pores occupied by the tissues, and render- 

 ing the corallum more solid ; and this is another means by which 

 the trees of coral growth, though of slender form, are increased 

 in strength and endurance. 



The facility with which polyps repair a wound, aids in carry- 

 ing forward the results above described. The breaking of a 

 branch is no serious injury to a zoophyte. There is often some 

 degree of sensibility apparent throughout a clump, even when of 

 considerable size, and the shock, therefore, may occasion the 

 polyps to close. But in an hour, or perhaps much less time, 

 their tentacles will have again expanded ; and such as were torn 

 by the fracture will be in the process of complete restoration to 

 their former size and powers. The fragment broken off, drop- 

 ping in a favorable place, would become the germ of another 

 coral plant, its base cementing by means of coral-secretions to 

 the rock on which it might rest ; or if still in contact with any 

 part of the parent tree, it would be reunited and continue to 

 grow as before. The coral zoophyte may be levelled by trans- 

 ported masses swept over by the waves ; yet like the trodden 



