THE ALGA 219 
SPIROGYRA,—ONE OF THE CONJUGATING ALG 
278. Occurrence. — Spirogyra, one of the commonest of 
the plants known as pond-scums, occurs widely distributed 
throughout the country in ponds, springs, and clear, slow 
streams. It is of a bright green 
color (yellowish green when 
producing spores). In warm 
sunny weather the masses usu- 
ally float, buoyed up by the 
Fic. 1538. A Group of Diatoms. Fie, 154. A Group of Desmids. 
A, Achnanthes; B, Cocconema; C, Merid-|A, Micrasterias; B, B’, Staurastrum 
ion; D, Pleurosigma. (two views); C, Closterium. 
numerous oxygen bubbles which the plants set free. It 
grows in unfrozen springs even in midwinter. Not in- 
frequently several species are found growing with the 
filaments intermixed. 
