236 PART III. THE CLASSIFICATION OF PLANTS. 



zoogonidia and zoospores ; sexual, either isogamous (planogametes), 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 rudimentary differentiation into 

 root and shoot ; reproduction, asexual by zoogonidia and zoospores, in 

 some cases ; sexual, isogamous (either planogametes or aplanogainetes), or 

 oogamous. 



Series V. Charoideas : plants multicellular ; body attached, differentiated into 

 stem (with apical growth), leaf, and root; reproduction, vegetative 

 by gemmaa, no zoogonidia or zoospores; sexual, oogamous, with multi- 

 cellular autheridium 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 imperfectly 

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

 in the life-history of each other or of higher Chlorophyceae. It appears, how- 

 ever, 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 Pleuro- 

 coccus, Oocystis, and Eremosphasra ; and such aggrr- 

 gate forms as Palmophyllum, Palmodictyon, Scene- 

 desmus. They generally grow in fresh water ; but 

 PJeurococcus grows on damp trees, stones, etc., and 

 Palmophyllum is marine. 



Order 2. Protococcaceae : cells isolated, or 



FIG. 166. Pleurococcus , . . , n - . 



mdgaris ( x 540) : cells di- aggregated into colonies of more or less definite form ; 

 viding. multiplication by cell-division is not general ; re- 



production, asexual by zoospores, or, less commonly, 

 sexual isogamous (planogametes). 



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

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

 Characium ; or inhabiting the tissues of higher plants, such as Chlorochytrium, 

 Phyllobium, Endosphaara ; (2) cells aggregated into mucilaginous masses cf 

 indeterminate form, e.g. Chlorosphasra 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, Paluiodactylon, Mischococcus, Hormotila, Oocardium), 

 or free-floating (e.ij. .Dictyosphasrium, Botryococcus). 



In some of these forms there is what is termed a Palmella-stage, in which 

 the cells multiply by division, surrounded by mucilage (e.g. Hormotila, 

 Characium). 



Isogamous reproduction by means of planogametes is known in Tetraspora, 

 Mischococcus, Chlorochytrium, Endosphaera, Phyllobium. The zygospore, on 

 germination, usually gives rise to one or two zoospores ; but in the endophytic 

 forms (Chlorochytrium, Phyllobium, Endosphasra) the still motile product of 

 conjugation, the zygozoospore, penetrates into the tissues of its future host, 



