Spirogyra - conjugating strands

Every year, usually just before their pond dries up, long strands of the thread alga, Spirogyra, line up. Tubes form between adjacent cells and the content of one flows through the tube into the other in a primitive form of sexual reproduction. As the nuclei from the two parent cells fuse, a hard outer shell forms around the zygote. This covering protects the zygote during periods of freezing and drying. When conditions are again favorable, out will hatch the first cell of a new strand of Spirogyra.