CORAL ALGAE 207 



in length. They usually branch dichotomously in one plane, 

 and the joints are flattened in the same plane and sometimes 

 expanded. There are some species, however, in which the 

 joints are cylindrical, as in Corallina. 



The joint of an Amphiroa has the same hard texture 

 and the same smooth and greasy surface as the Litho- 

 thamnion group of genera, and an examination with a lens 

 does not reveal any pores or other apertures, except the 

 openings of the conceptacles on those joints that happen to 

 be ripe. It is therefore typically a Nullipore. 



On microscopic examination of a joint, it is found to 

 consist of an enormous number of minute cells similar to 

 those of Lithothamnion although arranged rather differ- 

 ently. The nodes are composed of two or more rows of 

 these minute cells covered by a cortical layer of similar cells 

 differing from those of the joint in having very little or 

 no calcareous matter deposited in their walls, thus allowing 

 a certain amount of movement between one joint and the 

 next. 



The conceptacles are formed in small blister-like pro- 

 jections from the surface of the joints and are most con- 

 spicuous on the terminal branchlets of the plant. 



Corallina. — Another member of the family Corallin- 

 aceae is Corallina officinalis, a common alga in the rock pools 

 of our own coasts. Like Amphiroa on the Californian coast, 

 it is frequently found to cover the rocks with a miniature 

 forest of its slender delicate branches, of a pale pink or rose- 

 pink colour. On account of this habit and of its diminutive 

 size it was called by the older German writers the " Korall- 

 moos " or " Coral moss," a name which is very expressive 

 of its habit and of the soft velvety texture it seems to have 

 when felt by the hand immersed in the rock pool. But if this 

 " moss " is dried and examined with a lens, the coral-white 

 colour and the hardness of each separate joint reveal its 

 true position as a member of the family to which Amphiroa 

 and Lithothamnion belong. 



It is a jointed coral hke Amphiroa, and the joints are 

 usually cylindrical in form, i mm. in length and 0-5 mm. 

 in breadth. 



