2i8 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



i. Frond at first of a single series of cells, soon becoming a membrane. 



2. PRASIOLA. 



i. Frond at first of a single series of cells, soon becoming a terete multi- 

 cellular filament. 3. GAYELLA. 



i. SCHIZOGONIUM Kiitzing, 1843, p. 245. 



Frond normally a filament of a single series of cells, but at 

 times dividing longitudinally, so as to form ribbon-shaped 

 fronds, two or a few cells wide ; cells usually shorter than 

 their diameter, with central stellate chromatophore and one 

 pyrenoid ; asexual reproduction by akinetes and aplanospores. 



Usually terrestrial algae, normally filamentous, occasionally 

 dividing longitudinally, but not forming distinctly foliaceous 

 expansions. Gay, 1891, gives a broader extension to the genus, 

 adding 6". cri spurn, which appears here as Prasiola crispa. This 

 species produces filamentous fronds which may or may not 

 develope into membranes ; it connects the two genera, and it is 

 not easy to decide under which to include it. 



KEY TO THE SPECIES OF SCHIZOGONIUM. 

 i. Uniseriate filaments cylindrical ; multiseriate not uncommon. 



i. 5. murale. 



i. Uniseriate filaments moniliform or crenulate ; longitudinal cell- 

 division in a single cell or in a few successive cells. 



2. 5. crenulatum. 



1. S. MURALE Kiitzing, 1843, p. 246; Gay, 1891, p. 87, PI. 

 XIII, figs. 122-125. Forming a soft, tomentose stratum, bright 

 or dull green ; filaments flexuous, simple or rarely with short, 

 few-celled branches; cells usually 10-14/11 diam., occasionally a 

 little more or less ; often biseriate ; rarely pluri-seriate. On 

 moist earth, rocks, trees, etc. N. H., Alaska. Europe. 



Var. ALPINUM Farlow, P. B.-A., No. 70. Submerged; 

 forming long, loose, floating tufts in mountain brooks. N. H. 



2. S. CRENULATUM (Kiitz.) Gay, 1888, p. 72 ; 1891, p. 88, 

 PI. XIII, fig. 131. Forming a thin stratum, bright or dull 

 green ; filaments more or less moniliform or crenulate, rather 

 stiff, entangled, 11-14 A 1 diam., occasionally one or a few cells 

 duplicated; cells about as long as broad, more or less swollen 

 at the middle, walls between the cells quite thick. Fig. 76. 

 On moist wood, etc. N. H., Mass. Europe. 



2. PRASIOLA (Ag.) Meneghini, 1838, p. 36. 

 Fronds membranaceous, monostromatic, attached by short fili- 

 form prolongations, by the edge of the membrane, or by a thick- 



