PAPENFUSS: CLASSIFICATION OF THE ALGAE 179 



the cells exhibiting polarity as contrasted with the filamentous and frequently 

 heterotrichous habit of the forms placed in the Pleurocapsales. It is to be noted, 

 however, that these two authors do not in all instances agree in their assign- 

 ment of families to these two orders. 



The separation of the Hormogonales into Nostbcales and Stigonematales by 

 Fritsch is based on the occurrence of true branching and the heterotrichous 

 habit of the thalli in some forms (Stigonematales) as contrasted with the un- 

 branched or falsely branched condition of the filaments in others (Nostocales). 



The division of the bluegreen algae by Elenkin into a large number of orders 

 and families is an attempt to segregate the genera on the basis of small differ- 

 ences into seemingly clear-cut groups. Elenkin (1933) thus, for example, ele- 

 vates the Chroococcaceae to the rank of order and divides it into ten families 

 on the basis of the planes of division of the cells and the geometric form of 

 the colonies. Subdivision to the extent proposed by Elenkin is probably unwar- 

 ranted since it removes from one another forms which seemingly are so closely 

 related that some authors (e.g., Drouet and Daily, 1952) reduce them to a bare 

 few genera and species. 



The following synoptic arrangement of the orders and families is the author's 

 compromise of the various recent systems of classification of the Schizophyceae^^. 

 According to the current Code, the nomenclature of the Chroococcales and Cha- 

 maesiphonales starts with Linnaeus (1753), that of the Oscillatoriaceae (Hor- 

 mogonales) with Gomont (1892-1893), and that of all other Hormogonales with 

 Bornet and Flahault (1886-1888). 



Phylum SCHIZOPHYTA (Falkenberg) Engler (1892, p. 3) 

 Class ScHizopHYCEAE Colm (1880, p. 286) 



Syn.: Division Phycochromaceae Rabenhorst (1863, p. 1); Class Phycochromo- 

 phyceae Rabenhorst (1865, p. 1): Order Myxophyceae Stizenberger (1860, p. 18); 

 Cyanophyceae Sachs (1874, pp. 248, 251); Phycocyanophycees Marchand (1895, p. 

 11.) Non Schizophyceae Rabenhorst (1847, pp. v, 16) 

 Order CHROOCOCCALES Wettstein (1924, p. 79) 



Syn.: Entophysalidales Geitler (1925a, p. 223); Tubiellales Elenkin (1934, p. 

 56); Coccogonales (Thuret) Marchand orth. mut. Atkinson (1905, p. 163) 

 Family Chroococcaceae Nageli (1849, p. 40) 



Syn.: Coccobactreaceae Elenkin (1933, p. 19); Beckiaceae Elenkin 

 (1933, p. 19); Merismopediaceae Elenkin (1933, p. 19); Microcysti- 

 daceae Elenkin (1933, p. 19); Gloeocapsaceae Elenkin (1933, p. 19); 

 Coelosphaeriaceae Elenkin (1933, p. 19) ; Gomphosphaeriaceae Elenkin 

 (1933, p. 19) ; Woronichiniaceae Elenkin (1933, p. 19); Holopediaceae 

 Elenkin (1933, p. 19) ; Cyanidiaceae Geitler (1933, p. 624) 

 Family Entophysalidaceae Geitler (1925a, p. 235) 



Syn.: Chlorogloeaceae Geitler (1925a, p. 235) ; Tubiellaceae Elenkin 

 (1934, p. 56) 

 Order CHAMAESIPHONALES Wettstein (1924, p. 79) 



Syn.: Pleurocapsales Geitler (1925a, p. 238); Dermocarpales Geitler (1925a, 

 p. 238); Siphononematales Geitler (1925a, p. 238); Endonematales Elenkin 

 (1934, p. 57) 



Family Pleurocapsaceae Geitler (1925a, p. 238) 



Syn.: Chroococcidiaceae Geitler (1933, p. 623); Xenococcaceae Erce- 

 govic (1932, p. 138); Podocapsaceae Ercegovic (1932, p. 138) 



11. Several groups of organisms (other than the Beggiatoaceae) which have been 

 placed with the bacteria (Achromatiaceae, Vitreoscillaceae, Thriotrichaceae, Cyanochlo- 

 ridaceae) but which may be bluegreen algae, or at least include forms which probably 

 are bluegreen algae, are discussed by Pringsheim (1949). 



