248 PART IV. CLASSIFICATION. 



Series III. Siphonoidese : plants ccenocytic, unseptate or incompletely 

 septate ; non-motile ; the body may be a thalJus or may be differen- 

 tiated into stem, leaf, and root ; with or without apical growth ; 

 reproduction, asexual by zoospores ; sexual, either isogamous (plano- 

 gainetes), or oogamous. 



Series IV. Confervoideae : plants generally multicellular, filamentous, 

 branched or unbranched ; growth frequently intercalary, rarely 

 apical ; body attached or floating, a thallus, or sometimes with rudi- 

 mentary differentiation into root and shoot ; reproduction, asexual 

 by zoospores, in some cases ; sexual, isogamous (either planogametes 

 or aplanogametes), or oogamous. 



Series V. Charoidese : plants multicellular ; body attached, differentiated 

 into stem (with apical growth), leaf, and root ; reproduction, vegeta- 

 tive by gemmse, no zoospores ; sexual, oogamous, with multicellular 

 antheridium of complex structure. 



Series I. PROTOCOCCOIDE^E. The forms included in this series are very 

 various, and, inasmuch as their life-history is for the most part imper- 

 fectly known, it is uncertain to what extent they are independent, or are 

 only phases in the life-history of each other or of higher Chlorophycese. 

 It appears, however, that they may be fairly 

 classified into two orders : 



Order 1. Pleurococcaceae : cells isolated, or 

 aggregated into colonies of more or less definite 

 form ; multiply only by "cell-division ; no other 

 mode of reproduction. 



To this order belong such isolated forms as 

 Pleurococcus and Oocystis ; and such aggregate 

 FIG. l37.-Pl<mroeoccus forms as Palmophyllum, Palmodictyon, Scene- 

 vulgaris (x 640) : cells desmus. They generally grow in fresh water ; 

 dividing. but Pleurococcus grows on damp trees, stones, 



etc., and Palmophyllum is marine. 



Order 2. Protococcaceae : cells isolated, or aggregated into colonies of 

 more or less definite form ; multiplication by cell-division is not general ; 

 reproduction, asexual by zoospores, or, less commonly, sexual isogamous 

 (planogametes). 



This order includes (1) isolated unicellular forms, either free, such as 

 Chlorococcum, Halosphsera ; or attached at one end, such as Sciadium, 

 Characium ; or inhabiting the tissues of higher plants, such as Chloi-o- 

 ch3'trium, Phyllobium, Endosphaera ; (2) cells aggregated into mucila- 

 ginous masses of indeterminate form, e.g. Chlorosphsera which lies in or 

 on submerged fresh-water plants ; (3) cells aggregated into mucilaginous 

 masses of determinate form, the whole colony being generally attached at 

 some definite point (e.g. Apiocystis, Tetraspora), or free-floating (e.g. 

 Dictyosphserium, Botryococcus). 



In some of these forms there is what is termed a Palmel la-stage, in 

 which the cells multiply by division, surrounded by mucilage (e.g. Hor- 

 motila, Characium). 

 Isogamous reproduction by means of planogametes is known in some 



