Mar., 1922 classification of plants 131 



SYNOPSES OF THE SEVERAL PHYLA 



Phylum, ScHizoPHYTA. Fission Plants. 



I. Without a definite nuclear membrane and with a low type of chromatophore. 

 Class, Cyanophyceae. Blue-green Algae. 1000 species. 



A. Not filamentous; cells free or in masses or plates (superficial aggregates) ; 

 or the cell individuals with definite base and apex, in fruiting sometimes 

 forming a row of cells. Chroococcales. Chroococcaceae, Chamaesipho- 

 naceae. 



B. Cells arranged in definite filaments. 



L Filaments without hair-like tips, sometimes narrowed at the ends. 



a. Without heterocysts; free filaments commonly massed into flat 

 layers, sometimes several filaments enclosed in one common 

 sheath. Oscillatoriales, Oscillatoriaceas. 



b. With intercallary heterocysts. Nostocales. Nostocaces, 

 Scytonemataces, Stigonemataceas. 



2. Filaments with hair-like tips at one or both ends. Rivulariales. 

 Camptotrichaces, Rivulariacese. 

 IL With nuclear membrane and highly differentiated chromatophores; uni- 

 cellular or in colonies. Class, GLAucocYSTEiE. 20 species. Glaucocystales, 

 Glaucocystaceas. 



Phylum, Zygophyta. Conjugate Algas. 



L Cell walls impregnated with silica, composed of two valves; chromatophores 

 3'ellow or brown, rarely green, containing chloraphyll and diatomin and a 

 variable number of pyrenoids. Subphylum and class, Diatome^. Diatoms. 

 5700 species. 



A. Valves without a raphe or pseudo-raphe, with a concentric or ratiating 

 symmetry around a central point; valve view usually circular, polj^gonal, 

 or broadly elliptical in outline, rarely boat-shaped or irregular; con- 

 jugation unknown; cells without spontaneous movement. Mostly 

 marine plants. Eupodiscales. Round Diatoms. Eupodiscaceae, Sole- 

 niaceae, Biddulphiaceae, Rutilariaceae. 



B. Valves with a raphe or pseudo-raphe or with a sagittal line, with a zygo- 

 morphic or isobilateral or sometimes irregular symmetry; never centric; 

 valve view mostly boat-shaped or elliptic in outline; motile or nonmotile; 

 conjugation known in most groups. Mostly fresh water plants. 

 Naviculales. LongDiatoms. Fragillariacece,Surirellacese,Achnanthacece, 

 Naviculacese. 



IL Cell walls without silica, but with abundant development of gelatinous 

 pectose causing the plants to be slimy to the touch; chromatophores green, 

 with chlorophyll and one or more pyrenoids. Subphylum and class Con- 

 jugate. 2300 species. 



A. Thallus a filament, or commonly separating into single cells, mostly 

 flattened, the cell wall usually divided into two symmetrical halves; 

 cells mostly constricted at the middle, often of fantastic and beautiful 

 forms; cell contents mostly divided into symmetrical halves; conjugation 

 by the breaking open of the cell walls or by the formation of a primitive 

 conjugation tube. Desmidiales. Desmids. 2100 species. Spiro- 

 taeniaceae, Desmidiaceae. 



B. Thallus a simple filament, occasionally slightly branched, of cylindrical 

 cells, the cells not constricted in the middle, but sometimes the contents 

 divided into symmetrical halves; these latter forms distinguished from 

 the preceding order by the definite filament and prominent conjugation 

 tube; some species forming aplanospores. Zygnemales. Pond-scums. 

 200 species. One family, Zygnemaceas. 



