RHODOPHYCE.E, OR FLORIDE^ 235 



very rarely two or three small, round spores in series, 

 and they escape through the apical opening of the 

 stalked fruit. The tetraspores are very frequently 

 formed in stichidia. The family is a large one 

 consisting of a considerable number of genera of 

 conspicuous size and beauty of form, and some 

 of the genera, such as Polysiphonia, Z/aurencia, and 

 Dasya, are rich in species. Pleuro&ichidium, from 

 New Zealand, is however an exception, being a 

 minute epiphyte of quite different habit from the 

 other genera, but of essentially similar structure. 



The Geographical Distribution is world wide in the 

 sea ; some of the genera, such as Polysiphonia, have 

 a range as wide as that of the family. The British 

 genera. Bostrychia, Rhodomcla, Odonthalia, Laurencia, 

 Halopithys, Chondria, Polysiphonia,. Pterosiphonia, 

 and Dasya, are for the most part very common on 

 our shores. 



Ceramiece. 



This is one of the largest and most widely distri- 

 buted families of Red Seaweeds, and members of 

 it are everywhere common on coasts where Algal 

 life is found at all. The thallus consists of single 

 branched cell-filaments, sometimes with a cortex 

 formed of rhizoid filaments (not a true cellular cor- 

 tex). This false cortex is produced in the genera 

 allied to Callithamnion by the outgrowth of rhizoid 

 filaments from the basal cell of lateral branches, 

 while in Ceramium and its immediate allies, such 

 filaments spring from the upper ends (Fig. 78, ) 

 of the cells of the thallus, forming a peripheral 



