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HYDRODICTYON 



posed of a few loosely aggregated plants forming flat discs or 

 star-shaped plates (Fig. 105, ^). In other cases, we find spher- 

 ical and net-like colonies. The water net, Hydrodictyon, is a 

 common illustration of this latter arrangement (Fig. 105, D, E). 

 These plants occur in ponds and sluggish streams, forming sac- 

 like nets from a few inches to a foot in length, thdt are constructed 



Fig. 105. Colonial forms of unicellular green algae: A, Pediastrum, the 

 plants of the colony being arranged in a flat plate. B, a view of the outer 

 cells of the colony showing the formation of a new colony. C, one of these 

 new colonies. D, a plant of the water net containing a young colony. E, 

 enlarged view of one of the meshes of a net showing the geometrical arrange- 

 ment of the plants. 



in a very regular manner. The reproduction is quite character- 

 istic of many of the Volvocales. Zoospores are formed in large 

 numbers in any of the plants and after a period of motility, they 

 come to rest and arrange themselves into a new net inside of the 

 mother plant (Fig. 105, D). The walls of the mother plant soon 

 break down and the new colony is set free. Under different 

 conditions, smaller but similar bodies are formed which escape 

 from the mother plant. These bodies are gametes and incapable 

 of growth unless a fusion is effected between two of them. 



