plast a broad, folded axial plate, almost as long as the cell (sometimes 

 ulotrichaceous in appearance ) . Zygospores formed in the connecting 

 tube byscalariform conjugation, and extending into the gametangia; 

 oblong or rectangular-oblong; outer spore wall smooth, middle wall 

 with deep pits; 22-25/x in diameter, 33-38/x long (rarely longer). 



This species was once described as Mesogerron fluitans Brand and 

 included in the Ulotrichaceae because of its Ulothrix-like chloroplast. 

 Our specimens were found only in the vegetative condition, but 

 this plant is so distinctive that it can be assigned to Af . calospora. 



Rare in several lakes and Sphagnum bogs. The plants seems to 

 be confined to soft water habitats. Mich., Wis. 



SPIROGYRA Link 1820, p. 5 



Filaments long and unbranched, usually without basal-distal 

 diflFerentiation but sometimes with rhizoidal branches developing 

 laterally where the filament comes in contact with substrate. Cells 

 cylindrical, short, to very long in some species, with plane (even 

 and smooth), replicate, or colligate (exterior H-shaped piece) end 

 walls. Chloroplast a parietal band or ribbon which may be spirally 

 twisted 14 to 3 (rarely 8) turns, or may be nearly straight (as in 

 genus Sirogonium, not separated here); 1-16 chloroplasts in a cell. 

 Conjugation either lateral or scalariform, usually by the formation 

 of tubes, rarely by geniculate bendings of the filament so that 

 conjugating cells are brought into juxaposition. Zygospores formed 

 in one of the gametangial cells, which may become swollen, depend- 

 ing upon the species; zygospores ovate, subglobose, ellipsoid, or 

 oblong, with 3-layered wall, of which the middle layer may be 

 smooth or decorated and colored. Aplanospores uncommon, similar 

 to the zygospores in shape and wall markings; rarely aplanospores 

 alone occur. 



Spirogyra is the largest genus in number of species and the most 

 common of Zygnemataceae. It is identifiable in the field by its 

 bright green, cottony growths and its slippery mucilaginous texture. 

 In hand, a mass of filaments is easily drawn out into a long fine 

 thread. 



In deep cold springs and pools Spirogyra flourishes abundantly 

 and vegetatively, forming enormous green 'clouds' several feet in 

 diameter in favorable habitats. In shallow warm water it has a 

 tendency to form floating mats, with conjugation and subsequent 

 disintegration of the filaments occurring. During conjugation the 

 plant masses become dull, dirty-green or brownish, often with a 

 burnt-orange tinge, which is almost invariably macroscopic evidence 

 that reproduction is in progress. Some species of Spirogyra seem to 



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