rROTECTION A GAINST INJUR ] ; 73 



warrant that takes off at last the commoners about the base of 

 the tree ; it keeps growing and budding, and the tree thus 

 continues its increase. 



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

 would expose it, seemingly, to immediate wear from the waters 

 around it, especially as the texture is usually porous. But 

 nature is not without an expedient to prevent to some extent 

 this catastrophe. 



In the first place, there is often a peritheca over the dead 

 corallum — that is, an outer impervious layer of carbonate ot 

 lime, secreted by the lower edge of the series of dying polyps, 

 a fact in the Gouiopoi'a co/u?nna figured on page 32. Then, 

 further, the dead surface becomes the resting-place of number- 

 less small encrusting species of corals, besides NuUipores, 

 Serpulas, and some Mollusks. 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 becomes covered 

 with lichens and fungi, or, in tropical climes, with other foliage 

 and flowers ; so among the coral productions of the sea, there 

 are forms of life which replace the dying polyp. The process 

 of wear is frequently thus prevented. 



The older polyps, before death, often increase their coral 

 secretions also within, filling the pores as the tissues occupying 

 them dwindle, and thus render the corallum nearly solid ; and 

 this is another means by which the trees of coral growth, 

 though of slender form, are increased in strength and en- 

 durance. 



The facility with which polyps repair a wound, aids in 

 carrying forward the results above descri' ed. 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 again have expanded ; and 

 such as were torn by the fracture will be in the process of 

 complete restoration to their former size and powers. The 



