several pyrenoids; distal cells have a dense chloroplast of indefinite 

 shape. 



See Smith (1933, p. 457) for a discussion of the various opinions 

 concerning the taxonomic position of this genus. 



Schizomeris Leibleinii Kuetzing 1843, p. 247 

 PI. 7, Figs. 11-13 



Filaments stout, macroscopic, 20-25ft in diameter below, and as 

 much as 150/i, wide in the multiseriate upper portion of the frond. 

 Cells 15-30/i, in diameter. Zoospores formed in the upper limits and 

 escaping through an opening in the apex of the frond after interior 

 cell walls have disintegrated. 



Rather rare; in shallow water and marsh-like margins of both hard 

 and soft water lakes; also in several swamps. Mich., Wis. 



ORDER MICROSPORALES 



In this order there is only one family, which is monogeneric. The 

 plants are unbranched filaments, which are free-floating except when 

 young. The most distinctive feature is found in the structure of the 

 cell wall. The cells are cylindrical, with walls composed of two 

 H-shaped sections which adjoin in the midregion. In the thin-walled 

 species, however, this feature is scarcely discernible. When the fila- 

 ment dissociates, the cells fall apart into H-shaped sections because 

 the cleavage occurs at the points of juncture in the midregion rather 

 than at the cross walls. The end of a filament shows a half of the 

 H adjoined to the terminating cell. A thin, internal cellulose mem- 

 brane holds the wall sections together. Another characteristic which 

 differentiates this order is the morphology of the chloroplast. Al- 

 though it shows different specific expressions, its general form is 

 that of a parietal reticulum or perforated sheet, which may be dense 

 and padded or open and thin, covering almost all of the cell wall. 

 Often the padded character gives the appearance of there being 

 several chloroplasts. Starch accumulates as a food reserve, but there 

 are no pyrenoids. 



The absence of pyrenoids and the H-shaped wall sections are 

 characteristics in common with Tribonema in the Chrysophyta. In 

 that genus there are 2 to several disc-like, pale green chloroplasts, 

 and starch is not formed. 



Asexual reproduction is by biflagellate zoospores; gametes are 

 unknown. Aplanospores are frequently formed, especially when 

 water temperatures become high. 



[105] 



