56 SPECIES OF ALG/E. 



70. SPIROGYRA. 

 I. KEY TO THE STERILE PLANTS. 



As it is often difficult to determine the number of spiral bands 

 within a cell of Spirogyra, the following method, originally suggested 

 by "The Botanical Gazette," will be found exceedingly convenient. 

 Select a band near the middle of a cell, count those that cross it, add 

 one to the number, and the result will be the whole number of bands 

 in the cell. 



§ Membrane of ce'.ls folded in at the ends (a). 

 § " " " not folded in at the ends (y). 



a. Chlorophyll bands one only (U). 



a. " " two or more {g). 



b. Membrane of spore smooth (<r). 



b. " " " punctate (/). 



c. Filaments 28-33/^ in diameter; cells 3 to 10 times as long as wide, 



Grevilleana, 209 

 c. " 24-30// " " cells 3-9 times as long as wide, 



quadrata, 208 

 c. " i8-28/i " " (d). 



c. " 9-i8/t " " {e). 



d. Cells 10-25 times as long as wide; spiral of i J4 to 4 turns, 



Spreeiana, 208 



d. Cells 6-15 " " " " " spiral of 3>^ to 6 turns, 



Weberi, 208 



e. Cells 4-15 times as long as wide; spiral of 3-6 turns, 



tenuissima, 207 

 e. " 3-8 " " " " " spiral of 3-8 turns, inflata, 207 

 /. Diameter of filaments 36-40//; cells 6-12 times the diameter, 



calospora, 209 

 g. Spirals two (K). 

 g. Spirals three; cells 30-33// wide, 4-8 times as long as wide, 



Hassallii, 210 

 h. Cells i6-22// in dia., 4-8 times as long as wide, . Hilseana, 209 

 h. Cells 3o-33/< " " 4-8 " " " " " . Hassallii, 210 



h. Cells 36-45// in diameter (/). 



/. Cells 4-12 times as long as wide . insignis, 210 



i " 3-5 " " " « '< Hantzschii, 211 



j. One spiral in each cell (k). 



j. Two or more spirals in each cell (t). 



