GROUP I. THALLOPHYTA: ALGJS : CHLOROPHYCEJ]. 



249 



In some species, termed gynandrosporons, the filaments produce no anthe- 

 ridia, but only oogonia. Some of the cells of such a filament undergo trans- 

 verse division to form short cells which somewhat resemble antheridia. The 

 contents of each of these cells are set free as a single zoogonidium. termed an 

 androspore, intermediate in size and colour between the ordinary zoogonidia 

 and the spermatozoids, and resembling them in form. The androspore comes 

 to rest, attaching itself to 

 the wall of an oogonium 

 (Fig. 178), and germinates, 

 forming a small filament, 

 imown as a dwarf -male, 

 which consists of a root- 

 cell and two or three cells 

 above it ; each of these 

 upper cells is an anther- 

 idium, and its contents 

 are set free as a single 

 spermatozoid. 



On germination, the 

 contents of the oospore are 

 set free as four zoospores, 

 which resemble the zoo- 

 gonidia, and germinate in 

 the same manner. Fresh- 

 water : genera, (Edogon- 

 ium, Bulbochffite. 



Order 6. Coleochse- 

 taceae. Body filamentous, 

 branched, forming hemi- 

 spherical or disc-shaped 

 cushions on submerged 

 stones or parts of water- 

 plants ; the mode of 

 growth is essentially api- 

 cal, though in some forms 

 (C. scutata) the apical 

 cells constitute a marginal 

 series ; most of the cells 

 eventually develope the 

 peculiar sheathing hairs 

 which have suggested the 

 name of the family. 

 Fresh-water: Coleochaste, 

 the sole genus. 



The gonidaugia are un- 

 differentiated ; any cell 

 may set free its proto- 

 plasmic contents as a zoo- 

 gonidium with two cilia. 



FIG. 178. A (Edogonium ciliatum ^x 250). A Middle 

 part of a sexual filament with three oogonia (og) fertilised 

 by the dwarf -male plants (m), developed from zoogonidia 

 formed in the cell m at the upper part of the filament. 

 B Oogonium at the moment of fertilisation : o the 

 oosphere ; og the oogonium ; z the spermatozoid in the 

 act of forcing its way in ; m dwarf-male plant. C Ripe 

 oospore. D Piece of the male filament of (Ed. gemelli- 



parum, z spermatozoids. E Branch of a Bulbochcete, with 

 one oogonium still containing an oospore, another in the 

 act of allowing it to escape ; in the lower part an empty 

 oogonium. F The four zoospores formed from an oospore. 

 G Zocspore come to rest. (After Pringsheim.) 



