INTRODUCTION 



Gigartinales Chondrus, Gigartina, 



Iridaea 

 Rhodymeniales Rhodymenia 

 Ceramiales Bostrychia 



15 



Myxophyceae 

 (blue-green 

 algae; unicellu- 

 lar and filament- 

 ous forms lack- 

 ing a nucleus as 

 found in other 

 algae; fresh- 

 water, marine 

 and terrestrial) 



CYANOPHYTA 



Chroococcales 



Chamaesiphonales 



Pleurocapsales 



Nostocales 



Stigonematales 



Chroococcus, Gloeocapsa 

 Microcystis, Synecho- 

 coccus, Synechocystis 



Anabaejia, Anahaeniopsis, 

 Aphanizomenon, 

 Aulosira, Beggiatoa*, 

 Calothrix, Cyli^idro- 

 spermum, Gloeotrichia, 

 Nostoc, Oscillatoria, 

 Phorniidium, 

 Tolypothrix 



Mastigocladus 



such as Euglena pisciformis, possess chlorophyll and are 

 photosynthetic and yet require organic growth factors. '^^ It 

 is thus necessary to distinguish between the use of organic 

 substances as a source of energy and their use as growth 

 factors by organisms unable to synthesize particular meta- 

 bolites for themselves. The following is the relevant part 

 of a classification which recognizes this distinction.^'^' ^^* 



I. Nomenclature based upon energy sources. 



A Phototrophy: energy chiefly provided by photo- 

 chemical reaction. 



(i) Photolithotrophy: growth dependent upon exo- 

 genous inorganic hydrogen donors (e.g. most 

 green plants, in which water acts as the 

 hydrogen donor). 



(2) Photo-organotrophy: growth dependent upon 

 exogenous organic hydrogen donors (e.g. 

 photosynthetic bacteria belonging to the 

 Athiorhodaceae, in which organic substances 

 such as fatty acids act as hydrogen donors in 

 photosynthesis^"* ^) . 



