178 ^ CENTURY Of PROGRESS IN THE NATURAL SCIENCES 



It is to be regretted that both Geitler and Elenkin have burdened the already 

 involved nomenclature of the Schizophyceae with a number of unnecessary 

 names. These authors have violated the Code by renaming families whose cir- 

 cumscription they have changed but which still include the type of the rejected 

 family or, in the case of Geitler, by renaming families if the generic name from 

 which a family name was derived has been reduced to synonymy. 



Fritsch (1942, 1944, 1945) accepts in part Geitler's system of 1925 and di- 

 vides the Schizophyceae into the five orders Chroococcales, Chamaesiphonales, 

 Pleurocapsales, Nostocales and Stigonematales. In the division of the class into 

 five orders, the system of Fritsch corresponds closely to that of Geitler as 

 amended in 1942, except that Geitler at this time maintained the order Hormo- 

 gonales as a single taxon (as he had also done in 1930-1932) whereas Fritsch 

 recognizes in its place the two orders Nostocales and Stigonematales, as Geitler 

 had in 1925. 



Fritsch (1945) arranges the genera in 19 families, all of which, with the ex- 

 ception of the Cyanochloridaceae and Loefgreniaceae, were recognized also by 

 Geitler (1942), although the two authors do not always use the same names or 

 place the families in the same order. 



Fremy (1930, 1933), Copeland (1936), Huber-Pestalozzi (1938), Lindstedt 

 (1943), Skuja (1948), Smith (1950), Prescott (1951), and others accept only 

 the three original orders Chroococcales, Chamaesiphonales, and Hormogonales, 

 except that Copeland and Smith use the name Oscillatoriales Copeland (1936) 

 instead of Hormogonales. Drouet (1951), however, recognizes no orders in the 

 bluegreen algae and accepts only eight families. 



Evidently little agreement exists among students of the Schizophyceae as 

 regards the classification of the class. This disagreement is attributable not so 

 much to lack of knowledge of the morphology of these algae (although it seems 

 likely that cultural studies will yield information that will be useful in the 

 taxonomy of the group) as it is to the paucity of sharply defined characters and 

 the existence of intermediate types which preclude the establishment of clear- 

 cut taxa. The wide divergence in the systems proposed by the various specialists 

 on the group hinges primarily on the taxonomic value assigned to the available 

 characters. In his recognition of only eight families and the suppression of all 

 orders, Drouet is probably guided by the existence of transitional types, al- 

 though he has not yet presented the detailed arguments upon which his deci- 

 sions are based. 



The separation of the class into the three orders Chroococcales, Chamaesi- 

 phonales, and Hormogonales takes account of the structure of the thalli (uni- 

 cellular or colonial or pseudofilamentous in the Chroococcales, unicellular or 

 pseudofilamentous or filamentous in the Chamaesiphonales, multicellular and 

 filamentous in the Hormogonales) and the method of multiplication (vegeta- 

 tively by cell division or colony fragmentation in the Chroococcales, by endo- 

 spores in the Chamaesiphonales, by hormogonia and in some instances by aki- 

 netes in the Hormogonales). 



The division of the Chamaesiphonales into the two orders Chamaesiphonales 

 and Pleurocapsales by Fritsch (1942, 1944, 1945) and Geitler (1942, as Dermo- 

 earpales and Pleurocapsales) takes cognizance of differences in thallus organi- 

 zation — the Chamaesiphonales receiving plants which are unicellular and with 



