through and beyond the other branches to give a tapering, plumed 

 effect. Cells of the main axis 45-65/x in diameter; cells in the lateral 

 branches 6-10|U, in diameter. Chloroplast a narrow band about I/4 

 the length of the cell. 



Found several times in cold water at the bottom of soft water lakes 

 and in deep pools in Sphagnum bogs. Mich., Wis. 



MICROTH AMNION Naegeli in Kuetzing 1849, p. 352 

 Attached, branched filaments, forming a minute arbuscular thal- 

 lus on other algae, or on submerged aquatics such as mosses. Cells 

 cylindrical. Branches opposite or alternate, often curved, not taper- 

 ing to their apices but about the same diameter as the main axis 

 throughout; the first cross wall of the branch often at some distance 

 from the plane of origin. Chloroplast a parietal plate covering nearly 

 the entire wall; pyrenoid lacking. 



Key to the Species 



Main axis of the filament apparent only at the base of 



the thallus, soon lost in the ramifications _. - M. Kuetzingianum 



Main axis of the filament distinct throughout the thallus M. strictissimttm 



Microthamnion Kuetzingianum Naegeli in Kuetzing 1849, p. 352 



PL 11, Fig. 4 



Thallus highly branched and densely tufted, the main axis distinct 

 only at the base, soon becoming lost in the ramifications, which are 

 1 to several cells in length, the branches attenuated but very little 

 toward the apices. Cells cyUndrical; apical cell of branches bluntly 

 rounded. Diameter of axial cells about 4/x; length 10-15/i,. Chloro- 

 plast bright blue-green, covering most of the cell wall. 



This is a common species, apparently preferring soft water hab- 

 itats where there is a high concentration of organic acids. It is fre- 

 quently found in Sphagnum bogs. In Crystal Lake, Wisconsin, a 

 habitat of very soft water, this species was not found growing in 

 shallow water zones but was common on the moss (Drepanocladus) 

 which carpets the bottom at a depth of 35 feet. 



Attached to algae and submerged aquatics in many lakes and 

 swamps. Mich., Wis. 



Microthamnion strictissimum Rabenhorst 1859, No. 829 



PI. 11, Figs. 5, 6 

 Thallus minute, sparsely and alternately branched, the main axis 

 evident throughout; branches all ascending, neither curved nor 

 tapering, bluntly rounded at the apices. Cells cylindrical, with the 



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