EUPHYCOPHYTA 225 



the second hypothesis is the fact that Porphyridium is essentially a 

 soil alga, where it may occur in sufficient quantities to give a blood- 

 red colouring to the ground. 



* Ban GIACEAE : Porp/zj'ra (purple dye). Fig. 123 



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

 northern hemisphere from i5°to7i°N. and in the southern from 

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

 icity 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 hght and shade. The plant is flat and 

 membranous, whilst in the common species, P. umbilicalis, 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 at- 

 tached by means of a minute adhesive disc which is capable of 

 producing lateral extensions from which new fronds may be proU- 

 ferated. The disc is composed of long slender filaments together 

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

 the substrate swelling up, branching and producing suckers or 

 haptera which are apparently capable of penetrating dead wood or 

 the tissue of brown fucoids. In the latter case there is evidently a 

 capacity for epiphytism once contact is secured, and there is even 

 some evidence of partial parasitism. In California, Smithora 

 (formerly Porphyra) naiadum is an obligate epiphyte on Phyllo- 

 spadix and Zoster Uy two marine phanerogams. 



The gelatinous fronds of Porphyra^ which are normally mono- 

 stromatic although they become distromatic during reproduction, 

 are composed of cells that possess stellate chromatophores with a 

 pyrenoid, the process of nuclear division being intermediate be- 

 tween mitosis and amitosis. Reproduction is by means of mono- 

 spores, carpogonia, which have rudimentary trichogynes, and 

 antheridia, the carpogonial areas occupying a marginal position on 

 the thallus. 



In the Japanese P. tenera monospores are shed in considerable 

 numbers, 10,000 spores being produced from i sq. cm. of thallus. 

 These become attached to the substrate in a short space of time 

 and commence germination to a new plant one to two days after 

 fertilization. In sexual reproduction all the frond, except the basal 

 region, can produce antheridia. The species are dioecious or mono- 



