GROUP I. THALLOPHYTA : &LGM : CHLOROPHYCEJ1. 



241 



Order 2. Cladophoraceae. The body is incompletely septate and the 

 segments are coeuocytic ; it is filamentous, branched or unbranched, sometimes 

 differentiated into root and thalloid shoot, attached or free-floating, the shoot 

 with or without apical growth : reproduction, asexual by zoogonidia ; sexual, 

 isogamous, or oogamous. 



The order comprises the families Sphaeropleae. Cladophoreae, and Valonieze. 



Fam. 1. Sphceroplece : the body consists of floating unbranched filaments, 

 without distinction of base and apex, and 

 with intercalary growth. Each segment con- 

 tains numerous small chloroplastids as well 

 as some larger chloroplastids with pyrenoids. 

 Any segment of the body may become a 

 sexual reproductive organ, either an oogon- 

 ium or an antheridium, without any change 

 of form ; in the oogonium several oospheres 

 are formed by free cell- formation (see p. 121), 

 and likewise in the antheridium, after re- 

 peated nuclear division, a great number of 

 spermatozoids ; the oospheres are not ex- 

 truded, but are fertilised in the oogonium 

 by spermatozoids which enter through an 

 opening formed in the wall ; the oospore, at 

 first green, assumes a bright red colour, and 

 on germination sets free 2-8 zoospores, each 

 of which gives rise to a new filament : thus 

 the life-history indicates an alternation of 

 generations, the oospore representing the 

 sporophyte. Sphasroplea is the only genus, 

 and it comprises bat one species S. an- 

 indina. 



Fam. 2. Cladophorece : body filamentous, 

 generally attached by a basal root-segment, 

 branched (e.g. Cladopbora, Pithophora) or 

 xmbranched (e.g. Urospora, Chaetomorpha^ 

 llhizoclonium), with usually intercalary 

 growth (though it is apical in Cladophora and 

 Pithophora) ; each segment contains a peri- 

 pheral layer of chloroplastids (Fig. 172), 

 continuous or interrupted, in which are 

 scattered pyrenoids ; reproduction, asexual 

 by zoogonidia (except Ehizoclonium and 

 Pithophora) ; an isogamous sexual process 

 between planogametes has been observed in 

 Urospora and Cladophora ; reproductive cells 

 formed in all or any of the segments of the 

 body without special modification ; the zygo- 

 spore appears to develope directly into a new 



Fio. 172. Cladophora glomerate 

 (after Strasburger: x 510). A 

 coenocyte of the filament (chromic 

 acid and carmine preparation) : 

 nanucleus; chachloroplastid; the 

 polygonal chloroplastids form a 

 continuous layer, the outlines of 

 the individual plastids remaining 

 visible; p pyrenoids; v starch- 

 grains. 



plant (Cladophora), so that the sporophyte is not represented in the life-history. 



V. S. B. 



