euphycophyta 223 



Protoflorideae 

 This subdivision is sometimes known as the Bangioideae. The 

 plants are simple, unicellular, filamentous or membranous forms. 

 The cells contain a single axile chromatoplast. Growth of the 

 thallus is diffuse and not apical, and plasmodesmae between cells 

 are commonly lacking.^ Sexual reproduction is known for a number 

 of genera, but the carpogonium exhibits very Httie specialization. 

 The spermatia are formed by repeated divisions inside the mother 

 cell (e.g. Porphyra) or within special spermatangia {Erythrotrichia), 

 After fertiHzation reduction division takes place and the zygote 

 gives rise to haploid carpospores. Monospores form another means 

 of reproduction, being produced in one of three different ways : 

 (i) Those formed from differentiated sporangia, e.g. Erythro- 



trichia^ Erythrocladia. 

 (ii) Those formed from undifferentiated cells, e.g. Bangia. 

 (iii) Those formed by successive divisions of a mother cell, e.g. 

 Porphyra. 



Bangiaceae: Porphyridium cruentum (j)orphyridium^ diminutive of 

 purple dye; cruentum, blood red). Fig. 122 



This alga has had an extremely varied history, having been placed 

 at various times in both the Palmellaceae and Schizogoniaceae of 

 the Chlorophyceae, near to Aphanocapsa in the Myxophyceae, and 

 among the Bangiaceae in the Rhodophyceae where it finds a home 

 at present. The single cells are united into a one-layered, gelatinous 

 colony of a blood-red colour which is found on the soil. Cell divi- 

 sions take place in all directions, and when a cell divides the sheath 

 elongates to form a kind of stalk which eventually ruptures. Mono- 

 spores are produced as the only known means of reproduction other 

 than vegetative division. The cell contents round off and escape 

 from the cell envelope. So far no form of sexual reproduction has 

 been observed. In each cell there is one large chromatophore with 

 cyanophycin granules around the periphery and also a central 

 nuclear-like body, composed largely of anabaenin, which under- 

 goes a primitive form of mitosis at cell division. Whether this alga 

 represents a primitive form or else is a much-reduced type cannot 

 at present be determined. The principal argument in support of 



1 Recently the existence of plasmodesmae in some species has been reported, 

 so that this featture, formerly regarded as a major distinction, no longer exists. 



