Probably a growth form. Forming light green cottony masses 

 entangled in submerged roots and sticks. Occurring with the typical 

 plant. 



Tribonema minus (Wille) Hazen 1902, p. 185 

 PI. 96, Figs. 12, 13 



Filaments slender; cells slightly inflated to subcylindrical, 5—6/1, 

 wide, 23—27/1 long (rarely longer); chromatophores 2—4 relatively 

 large parietal disc-like plates, symmetrically arranged about the 

 wall (as in T. aequale Pascher). 



In shallow water of lakes and ponds; often in water with humic 

 acids. Wis. 



Tribonema utriculosum ( Kuetz. ) Hazen 1902, p. 186 



PI. 96, Figs. 14-16 



Filaments long or short, fragmenting easily; cells stout with 



relatively heavy walls, clearly showing the overlapping of the 2 



wall pieces in the midregion of the cell; chromatophores many 



irregular discs; cells lO-lY/x in diameter, 15-53.5/i. long. 



Forming loose cottony masses in shallow water of lake margins, 

 swamps, and marshes; tychoplanktonic. Mich., Wis. 



ORDER HETEROSIPHONALES 



The plants which compose this small order are vesicular, growing 

 on moist soil with subterranean rhizoidal portions. There are numer- 

 ous small chromatophores and nuclei. Although pyrenoids are re- 

 ported, the food reserve is oil rather than starch. Reproduction is 

 by zoospores, aplanospores, or by hypnospores which are formed 

 underground in the rhizoidal portions of the thallus. There is 1 

 family. 



FAMILY BOTRYDIACEAE 



Characteristics as described for the order. This family contains 1 

 genus, and of the 2 species reported from the United States one 

 occurs in our collections. 



BOTRYDIUM Walhoth 1815, p. 153 



A macroscopic, unicellular coenocyte growing on moist soil, 

 vesicular and globose above, narrowed below to form subterranean 

 rhizoidal branches; chromatophores numerous yellow-green discs; 

 food reserve oil and leucosin; spores formed in the underground 

 portions of the thallus. 



Botrydium Wallrothii Kuetzing is to be expected in this region 

 but has not been reported. The membrane of the vescicle in this 



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