252 



PART IV. CLASSIFICATION. 



extruded, and has a hyaline receptive spot directed towards the opening 

 of the oogonium. 



Vaucheria forms the green felt which covers the soil in damp flower- 

 pots or other moist situations. Aquatic species occur in ditches, etc., 

 often forming a thick scum on the surface. 



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

 segments are coenocytic ; it is filamentous, branched or unbranched, some- 

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

 the shoot with or without apical growth : 

 reproduction, asexual by zoospores ; sex- 

 ual, isogamous, or oogamous. 



Fam. 1. SphceropJece : the body consists 

 of floating unbranched filaments, without 

 distinction of base and apex, and with 

 intercalary growth. Each segment con- 

 tains numerous small chloroplastids. 

 Any segment of the body may become 

 a sexual reproductive organ, either an 

 oogonium or an antheridium, without 

 any change of form; in the oogonium 

 several oospheres are formed by free cell- 

 formation (see p. 87), and likewise in the 

 antheridium, after repeated nuclear divi- 

 sion, a great number of sperm atozoids ; 

 the oospheres are not extruded, but are 

 fertilised in the oogonium by spermato- 

 zoids 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 fila- 

 ment. Sphseroplea is the only genus, and 

 it comprises but one species S. annutina : 

 it inhabits fresh water. 



Fam. 2. Cladophorece : body filamentous, 

 generally attached by a basal root-seg- 

 ment, branched (e.g. Cladophora) or un- 

 branehed (e.</.Chaetomorpha), with usually 

 intercalary growth (though it is apical 

 in Cladophora) ; each segment contains a 

 peripheral layer of chloroplastids (Fig. 

 143), Continuous or interrupted, in which 

 are scattered pyrenoids ; reproduction, 

 asexual by zoospores in some forms (e.g. 

 Cladophora), or vegetatively (e.g. Pitho- 

 phora); an isogamous sexual process be- 

 tween planogametes has been observed in 

 Gladophora: reproductive cells formed in 



FIG. 143. Cladophora glomerata 

 (after Btrasburger: x 540). A 

 coenocyte of the filament (chromic 

 acid and carmine preparation) : 

 n a nucleus ; ch a chloroplastid ; the 

 polygonal chloroplastids form a 

 continuous layer, the outlines of 

 the individual plastids remaining 

 visible; p pyrenoids; v starch- 

 grains. 



