2i8 RHODOPHYCEAE 



*Bangiaceae: Porphyra (purple dye). Fig. 143. 



This is a genus which has a very wide range as it extends in the 

 northern hemisphere from 40° to 71° N. and in the southern from 

 the Cape of Good Hope to 60° S. It has a variable seasonal 

 periodicity in English waters where its presence is determined by 

 the amount of water available, e.g. whether the site is subject to 

 spray, together with the intensity of light and shade. The plant is 



Fig. 143. Porphyra. A, thallus ( x |). B, attachment disk with three primary 

 blades and four (1-4) secondary. C, formation of carpospores. D-H, formation 

 of antherozoids in P. tenera. (A, D-H, after Ishikawa; B, C, after Grubb.) 



flat and membranous, whilst in the common species, P. umhilicalis, 

 there are a number of growth forms, the shape, width and length 

 of the various forms being determined by the age of the plant, the 

 height above mean sea-level and the type of locality. The plants 

 are attached by means of a minute adhesive disk which is capable 

 of producing lateral extensions from which new fronds may be 

 proliferated. The disk is composed of long slender filaments 

 together with some short stout ones, those near to or in actual 



