COMMON POND-SCUM. 



Spirogyra. 



THALLOPHYTES; ALG^J CHLOROPHYCE^E. 



PRELIMINARY. 



THE members of this genus are abundant in stagnant 

 water everywhere, forming bright yellow-green scums of 

 great extent, sometime diffused beneath the surface, or 

 occasionally in running water attached to stones. They 

 may be distinguished readily from all other scum-pro- 

 ducing plants, except from a few of their close allies, in 

 having a slippery feel, and being composed of long 

 unbranched filaments, which string out like wet hair 

 when withdrawn from the water. The allied kinds, 

 which cannot be separated by this test, will at once be 

 distinguished when placed under the microscope by 

 possessing no spiral chlorophyll bands as does Spirogyra. 

 When growing vigorously the masses of Spirogyra are 

 an intense light green; when beginning to form spores 

 they turn yellowish, and look very uninviting; but as 

 the characteristics which distinguish the species are 

 largely drawn from the reproductive condition, the col- 

 lector soon learns to regard these unsightly objects with 

 favor. 



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