238 Science of Plant Life 



by surface water. Several thousand different species of algae 

 are concerned in the formation of pond scums. Micros pora 

 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- and energy-producing pro- 

 cesses. 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 causes the 

 filament to increase in length. This long, slender line of 

 cells is easily broken, and the plant may be multiphed by the 

 breaking of the filaments into parts. 



Spores in Microspora. Microspora produces swimming 

 spores and resting spores. These are special cells that re- 

 produce 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, 

 hairlike 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 con- 

 tinues 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 



