PAPENFUSS: CLASSIFICATION OF THE ALGAE 175 



of the Scliizophyceae. Stizenberger remarked that these algae were distinguish- 

 able from other algal orders by their pigments. 



Rabenhorst (1863, p. 1) established a division for these algae which, on the 

 basis of color, he named Phj^cochromaceae. As one of the features of the group, 

 Rabenhorst mentioned the absence of a nucleus in the cells, a character pre- 

 viously remarked upon by Nageli (1849, p. 45) with reference to some of the 

 unicellular members of the assemblage. 



Rabenhorst credited the group with six families, viz., Chroococcaceae, Os- 

 cilla[to]riaceae, Nostocaceae, Rivulariaceae, Scytonema[ta]ceae, and Sirosi- 

 phonaceae (= Stigonemataceae), all of which are still accepted, although usually 

 with modified circumscriptions. 



In 1865 Rabenhorst regarded tlie bluegreen algae as a class and changed 

 the divisional name Phycochromaceae, which he had given them in 1863, to Phy- 

 cochromophyceae. At this time Rabenhorst divided the class into two orders: 

 "Ordo I. Cystiphorae," in which he placed the family Chroococcaceae, comprised 

 of unicellular and colonial forms, and "Ordo II. Nematogenae," to which he 

 referred the remaining five families of his treatment of 1863, all of which in- 

 cluded filamentous forms. 



On account of their blue pigment, Sachs (1874) named these algae Cyano- 

 phyceae. Because of the appropriateness of this designation and because of the 

 fame of Sachs and his textbook, the name Cyanophyceae immediately gained 

 favor among botanists, and it is still used by many. 



Cohn (1880, p. 286) gave these algae the name Schizophyceae.^*' He re- 

 garded them as a group coordinate with the bacteria (which he in 1872 [a] had 

 named Schizomycetae) and placed both groups in his order Schizosporeae, as 

 he had first done in 1872 (a and b). That there existed a relationship between 

 these two groups of organisms had already been pointed out by Cohn as early 

 as 1854. 



Engler (1892) divided the thallophytes into two divisions, the Myxothallo- 

 phyta and the Euthallophyta. Under the latter he had a number of subdivisions, 

 one of which was Schizophyta, to which he referred the two classes Schizophy- 

 ceae and Schizomycetes. Without giving the reference, Pringsheim (1949, p. 

 48) and others credit Cohn with the name Schizophyta, but I have been un- 

 able to find this designation in Cohn's publications. It apparently was used 

 for the first time by Falkenberg (1882, p. 162) as the name of an order com- 

 prising both the bluegreen algae and the bacteria. 



In conformity with the views of Cohn and the system of Engler, which has 

 had many adherents down to the present, the bluegreen algae are here regarded 

 as constituting a class, the Schizophyceae, coordinate with the bacteria (class 

 Schizomyceteae) in the phylum Schizophyta. It should be pointed out, however, 

 that many biologists do not believe that these two (or several) groups of organ- 

 isms are related. This latter view has been particularly well defended by Prings- 

 heim (1949), to whom the reader is referred for a detailed discussion of the 

 question (see also Stanier and van Niel, 1941). 



Although the characters which point to an af^nity between bacteria and 



10. It is to be noted, however, that Rabenhorst (1847, pp. V, 16) had previously used 

 the designation Schizophyceae for a "suborder" of algae comprising the diatoms and 

 desmids. 



