Spirogyra is a filamentous algae that may become so abundant during the summer that it forms the so-called 'pond scum', the familiar thick green masses in a pond. But under the microscope these organisms are beautiful. Like their relatives the desmids they are conjugating green algae. You can often see them conjugating. 2 strands of Spirogyra will make connections by small tubes and exchange genetic material. Note the chloroplasts in a helix and the nucleus in the center of the cell.