Microspora, the only genus, is sometimes included in the order 

 Ulotrichales. The characteristics of Microspora species are so dis- 

 tinctive, however, that placing them in a separate order seems 

 justifiable ( Heering, 1914; et al. ) . 



FAMILY MICROSPORACEAE 

 MICROSFORA Thuret 1850, p. 221 

 Plants unbranched, unattached filaments of uniseriately-arranged 

 cylindrical, or slightly swollen, cells ( attached filaments are not un- 

 known, however). Cell walls thin in some species; in others thick 

 and lamellate, composed of 2 sections overlapping in the midregion. 

 Filaments fragmenting readily when mature by the separation of the 

 walls at their point of juncture, so that H -shaped sections and frag- 

 ments are formed. Chloroplast either a dense and irregularly padded 

 parietal plate or net, or an open meshwork or "rosenkranz" form of 

 reticulum; pyrenoids lacking. Cells frequently forming aplanospores 

 or akinetes, the latter globose, with much-thickened walls. 



Key to the Species 



1. Walls thin, Im or less in thickness; juncture of the wall 

 sections in the midregion of the cell not cleady evident 

 except upon fragmentation of the filament — - — 2 



1. Walls 1.5-2.5m thick, often lamellate; junctiure 



of the wall sections clearly evident --- - 6 



2. Chloroplast an open meshwork, stringy, but 



sometimes thickened in places — — - - 3 



2. Chloroplast a parietal, perforated plate or close 



meshwork covering most of the cell wall - - - 4 



3. Cells distinctly cylindrical, 14-17m in diameter, 22-35ai long ,., M. jioccosa 



3. Cells quadrate or short-cylindric, 11-14m in diameter 



and up to 22m long ^- Willeana 



4. Cells about 9/j. in diameter, 1-3 times the diameter 



in length; chloroplast a granular plate M. stagnorum 



4. Cells narrower, and usually shorter; chloroplast dense 5 



5. Cells 6.7-9.5m in diameter, quadrate ( sometimes as much 



as twice the diameter in length); constricted at the cross walls M. tumidula 



5. Cells 5.5-7.0m in diameter, shorter than wide, or quadrate; 



not constricted at the cross walls M. quadrata 



6. Filaments 21.5-40^ in diameter - -- '^ 



6. Filaments 20m or less in diameter -- 8 



7. Filaments 21.5-27/^ in diameter, up to twice the diameter in 



length; shghtly constricted at the cross walls -- -- M. amoena 



7. Filaments 26-33/ii in diameter (rarely more), cells usually 



cylindrical, I-IV2 times the diameter in length M. crassior 



8. Cells cyhndrical, 8-12^ in diameter, up to twice the 



diameter in length M. pachyderma 



8. Cells quadrate or cylindric, 13-20^ in diameter - 9 



[106] 



