516 Reproduction in Fresh- Water Alge. (September, 
The members of the genus Spirogyra are very common in 
fresh-water ponds, making up much of the filamentous “ scum ” 
often seen on the surface. They are easily recognized under the 
microscope by their green spiral bands of chlorophyll (Figure 87, 
a, and still more enlarged in b). New individuals are formed by 
the simple division of the old cells by means of a partition wall 
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(Fre. 87.) REPRODUCTION OF SPIROGYRA. 
through the middle; each half then grows to the normal size 
and again divides, thus increasing the length of the filament. 
Conjugation takes place between the cells of adjoining filaments. 
The first perceptible change is a contraction in the spirally sik 
ranged protoplasmic contents into a somewhat compact and irreg- 
ular mass, followed by a bursting of the cell-wall, out of which a 
process is pushed, which, meeting with another similar one from 
