120 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



By the middle of the last century, a comparatively large number of genera 

 of unicellular green algae — both flagellated and nonfiagellated forms — had been 

 described, mostly by Ehrenberg (1838 and earlier), Nageli (1849), and others. 

 Many of these genera, however, were regarded as animals, the gutless stomach 

 animalcules of Ehrenberg. 



In 1819, Lyngbye described the genus Palmella and in 1824 C. Agardh de- 

 scribed Protococcus. Since these two genera of unicellular algae were comprised 

 of nonmotile forms (cf., however, Silva and Starr, 1953, regarding Protococcus) 

 they were accepted as algae rather than animals from the beginning. Recogniz- 

 ing the distinctiveness of PahneUa and Protococcus as contrasted with the gen- 

 era that constituted the Ulvaceae (which received mostly membranous forms) 

 and the Cpnfervaceae (which received mostlj^ filamentous forms), Endlicher 

 (1843) created for them and various other unicellular genera the suborder 

 Palmellae, which he placed in the "order" Confervaceae. The Palmellae were in 

 turn subdivided by Endlicher into the two tribes Protococcoideae (which re- 

 ceived Protococcus) and Coccochloreae (which included PahneUa). 



Kiitzing (1833b) was the first to recognize the differences between the dia- 

 toms and the desmids, for the latter of which he established the family Des- 

 midiaceae. He (1843, 1845, 1849) placed this family in a separate group Cha- 

 maephyceae (dwarf algae), which he (1845) assigned to the Chlorophyeeae. 

 The Chamaephyceae also received, among others, the Palmellae, which Kiitzing 

 regarded as a family. Hassall (1845) erected a separate family Protococceae 

 for Protococcus and several other genera. 



Since these early beginnings, the Palmellaceae and Protococcaceae have had 

 an extensive and involved taxonomic history. For a long time they functioned 

 as a catch-all for many different kinds of unicellular and colonial algae. 



Siebold (1849), Nageli (1849), Braun (1851), and Colin (1852, 1854) re- 

 garded as algae certain unicellular and colonial motile green organisms such as 

 Chlaynyclomonas, Gonium (first recognized as an alga by Turpin, 1828a, pp. 322- 

 329), Panclorma, StepJianosphaera, and Volvox (all members of the Volvocales). 

 Cohn at first (1852) placed these organisms in the "order" Palmellaceae but in 

 1856 considered them as constituting the family Volvocaceae. Rabenhorst ( 1863, 

 1868) grouped the Volvocaceae along with the Palmellaceae and Protococcaceae 

 in a common order which he (1868) called Coccophyceae. 



The relationship between the Zygnemataceae and the Desmidiaceae was recog- 

 nized by Nageli (1849) and others but it was De Bary (1858b) who first fur- 

 nished conclusive proof of this. He united these two groups in a "family" 

 Conjugatae. 



In his important work on the freshwater algae of Europe, Rabenhorst 

 (1868) divided the green algae in accordance with the system of Stizenberger 

 (1860) into four orders: (1) Coccophyceae, with the families Palmellaceae, Pro- 

 tococcaceae, and Volvocaceae; (2) Zygophyceae, with the families Desmidieae and 

 Zygnemeae; (3) Siphophyceae, with the families Hydrogastreae (^Botrydia- 

 ceae) and Vaucheriaceae; and (4) Nematophyceae, with the families Ulvaceae, 

 Sphaeropleaceae, Confervaceae, Oedogoniaceae, Ulotrichaceae, Chroolepidiaceae 

 (=Trentepohliaceae), and Chaetophoraceae. The separation of the Chlorophy- 

 cophyta into the four orders recognized by Stizenberger (but later, for example, 

 by De Toni [1889] and Wille [1890-1891], usually called Protococcoideae, Con- 



