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Light micrograph of a colony of ^IHydrodictyon ^Isp. ^i, a freshwater green alga also known as the water- net. Each individual cylindrical cell typically connects with 6 neighbours (5-8 are also known) to form a three- dimensional network. ^IHydrodictyon^i is a coenobium or determinate colony, which means that the total number of divisions & thus the number of cells making up the colony is fixed at the time of the origin of the colony & cannot be extended. Unlike indeterminate colonies, it is not simply an aggregate of cells with unlimited potential for cell division. Magnification: x100 at 35mm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/POWER AND SYRED/SCIENCE PHOTO LIBRARY)