56 Chlorophycece 



Order II. Chcetophorales. Thallus filamentous, sometimes 

 simple, but more often branched. Cells uninucleate ; 

 chloroplasts parietal, generally single and with pyre- 

 noids. Sexual reproduction either isogamous or 

 heterogamous. Mostly freshwater. 



Order III. Ulvales. Thallus expanded, membranous, paren- 

 chymatous, attached when young. Cells uninu- 

 cleate ; chloroplasts single, parietal, with one pyre- 

 noid. Sexual reproduction isogamous. Mostly 

 marine. 



Order IV. Schizogoniales. Thallus filamentous, sometimes 

 parenchymatous, or expanded by fusion of filaments 

 in one plane. Chloroplast single, central and 

 substellate, with one pyrenoid. Mostly subaerial. 



Order V. Microsporales. Thallus filamentous, unbranched. 

 Cells uninucleate. with a large, parietal, reticulated 

 or band-like chloroplast, destitute of pyrenoids. 

 Exclusively freshwater. 



Order VI. Cladophorales. Thallus filamentous, simple or 

 branched, incompletely septate. Segments large 

 with numerous parietal chloroplasts each with a 

 pyrenoid. Sexual reproduction isogamous or hetero- 

 gamous. Marine or freshwater. 



Order VII. Siphonece. Thallus filamentous and coenocytic, 

 unseptate, consisting of one large branched cell 

 with many nuclei. Chloroplasts numerous, without 

 pyrenoids. Sexual reproduction heterogamous. 

 Mostly marine. 



Order VIII. Conjugates. Thallus unicellular or filamentous. 

 Cells uninucleate ; chloroplasts single or several, 

 usually large and of some definite shape, with 

 pyrenoids. Sexual reproduction by isogamous 

 aplanogametes. Exclusively freshwater. 



Order IX. Protococcoidece. Small unicellular, multicellular 

 or colonial Alga3. Cells uninucleate or coenocytic ; 

 chloroplasts very variable in form, size and disposi- 

 tion, with or without pyrenoids. Sexual reproduc- 

 tion of an isogamous or heterogamous character is 

 known in some. Almost exclusively freshwater. 



