200 CORALS 



vegetable kingdom is the examination of the surface of a 



dried specimen with a magnifying glass. If the surface is 



found to be entirely imperforate and seems to be smooth 



and even greasy to the touch, it is certainly a plant and 



not an animal coral. It is probable, however, that no coral 



has a surface which is really imperforate, and if a little chip 



of the surface of such a coral be examined with a high power 



of the microscope, the minute apertures of the superficial 



layers of cells may be discovered. The coral Algae, however, 



may be in fructification, and in that case the surface will 



exhibit a number of more or less prominent convexities — 



projecting conceptacles — and at the summit of each of these 



convexities there is a pore of larger size, that is to say a 



pore visible under a low-power magnifying glass (Fig. loi). 



In such cases, if there is any doubt as to the nature of the 



coral, the hard close texture of vegetable coral — if it belongs 



to theCorallinaceae — and the characteristic cellular structure, 



when seen in section under the microscope, are sufficient to 



separate it definitely from any kind of animal coral and 



establish it as a plant. The next observation to make 



presents no difficulty and does not require the help of the 



magnifying glass. It is to determine whether the thallus 



is continuous in growth or jointed (compare Figs. 102 and 



106). If it is continuous in growth it belongs to one section 



of the family Corallinaceae, which may be called section A. 



If it is jointed it belongs to the other section (B) of the 



Corallinaceae or to another Order of Marine Algae (see 



p. 210). 



Section A of the Corallinaceae has been divided by 

 systematists into a large number of genera and sub-genera, 

 many of which are comparatively rare and will not be re- 

 ferred to in this chapter. The most abundant and widel}' 

 distributed of the unjointed Corallinaceae belong to the 

 genera Melobesia, Lithothamnion, and Lithophyllum. 



The thalli of these three genera are so variable in form 

 that it is difticult to give any general definition of any one 

 of them that can be relied upon as a guide to the ready 

 determination of any given specimen. Many overlapping 

 forms occur which can only be definitely placed in their 



