Besides conjugation, described above, akinetes (thick- walled rest- 

 ing cells formed by modification of vegetative cells) or partheno- 

 spores ( aplanospores ) may occur. The latter are thick- walled, zygo- 

 spore-like bodies formed within cells independent of conjugation. 



Reproductive material often can be identified in the field, espec- 

 ially in Spirogijra, Motigeotia, and Zijgnema, by the foamy, brownish 

 or 'dirty' appearance of the plant masses. In many forms conjugation 

 regularly occurs in surface mats of filaments, each species fruiting 

 in its own season. 



Key to the Genera 



1. Cells with 2 broad, disc-like chloroplasts, mostly axial but in part 



parietal; cell sap deep purple (rarely colorless) ** Pleurodiscus 



1. Cells with other types of chloroplasts; cell sap colorless (but 



Hlac or purplish-brown in Mougeotia capucina ) 2 



2. Chloroplasts parietal ribbons (usually with laciniate or crenate 

 margins ) , spiral ( rarely nearly straight ) , with several 



to many pyrenoids in a single series - Spirogyra 



( including Sirogonitim ) 



2. Chloroplasts axial, shaped otherwise, broad bands, stellate bodies, 

 elongate pads, or axial polster (cushion-shaped) bodies 3 



3. Chloroplasts axial plates or bands, broad and filling the width of 



the cell in some; pyrenoids none, or 2 to many, in 1 row or scattered 4 



3. Chloroplasts (usually 2) axial, star-shaped or pad-like bodies 7 



4. Chloroplasts without pyrenoids Mougeotiopsis 



4. Chloroplasts with pyrenoids - 5' 



5. Conjugating cells formed by a portion of the 



vegetative cell cut off from one end ...^..''Temnogametum 



5. Conjugating cells involving the entire vegetative cell 6 



6. Conjugating cells becoming filled with pectic substances Dehanja 



6. Conjugating cells not becoming filled with pectic substances, 



often containing granular residues Mougeotia 



7. Chloroplasts 2 central, polsterform bodies (without, or with very 

 short, radiating processes); cytoplasmic granular material left in 

 conjugating cells and in sporangia — ■_ Xygogonium 



7. Chloroplasts 2 star-shaped bodies in each cell 



(radiating processes long) ^ 



8. Conjugating cells becoming filled with pectic substances; 

 zygospores always formed in the tube, spheroidal or mostly 



quadrate, flattened or polsterform in side view Zygnemopsis 



8. Conjugating cells not becoming filled with pectic substances; 

 zygospores formed in the tube or in one of the 

 gametangia, globose, ovate, or somewhat cylindric— - Zygnema 



DEBARYA (Wittr.) Transeau 1934, p. 203 



Filaments of slender, cylindrical cells; chloroplast a narrow axial 

 plate containing 2-8 pyrenoids (these sometimes increasing in 

 number prior to conjugation); conjugation scalariform by pro- 

 tuberances from both gametangia; zygospores variable in shape, 



[ 296 ] 



