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 cells folded in at the ends (a). 

 " " " not folded in at the ends (j). 



a. Chlorophyll bands one only (b). 



a. " " two or more (g). 



b. Membrane of spore smooth (c). 



b. " " " punctate (/). 



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



Grevilleana, 209 

 c. " 24-3<D/< " (t cells 3-9 times as long as wide, 



quadrata, 208 

 c. " 18-28;* " " (d). 



c, " 9-1 8/t " " (e). 



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



Sprceiana, 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 

 . Spirals two (Ji). 

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



Hassallii, 210 



h. Cells 16-22 ^ in dia., 4-8 times as long as wide, . Hilseana, 209 

 h. Cells 30-33/* " " 4-8 " " u " " . . Hassallii, 210 

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



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



/ " 3-5 " " " " " Hantzschii, 211 



j. One spiral in each cell (/). 



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



