The x\lgae 449 



not in the green scums, but in the presence of certain disease- 

 producing bacteria that may have been carried into the ponds 

 by surface water. Several thousand different species of algae 

 are concerned in the formation of pond scums. Microspora may 

 be studied as an example of the more simple filamentous forms. 



Microspora. The Microspora plant is a filament made up of 

 cylindrical or barrel-shaped cells placed end to end. Each cell 

 carries on all its own food-producing and energy-producing 

 processes. During early spring, as food is manufactured, the 

 cells enlarge and divide. The division is always in the same 

 direction, however, and the cells remain attached to each other, 

 so that the growth and division of the cells cause the filament to 

 increase in length. This long, slender line of cells is easily broken, 

 and the plant may be multiplied by the breaking of the filaments 

 into parts. 



Spores in Microspora. Microspora produces swimming spores 

 and resting spores. These are special cells that reproduce the 

 plant. A swimming spore is formed by the contents of a cell 

 in the filament contracting into an ovoid body. At one end of 

 this body two cilia, which are small, hair-like propellers, are 

 developed. The wall of the original cell then breaks and the 

 swimming spore is set free. After swimming about in the water, 

 for a short time, it becomes attached to some object under 

 water, loses its cilia, and grows into a cylindrical vegetative 

 cell. This cell then continues to grow and divide until a new 

 filament is formed. The advantages of swimming spores are 

 that they multiply the plant, and by their ability to swim they 

 enable the plant to spread to new locations that it might not 

 reach without these motile cells. 



The resting spores are usually formed in the spring after the 

 active period of vegetative growth has passed. At this season 

 the cells in the filament stop dividing and food accumulates in 

 the form of starch and protein granules. The protoplasm in 

 each cell then contracts into a spherical form and secretes a heavy 



