244 



Science of Plant Life 



FIG. 146. Food relations of aquatic life. 



weeks or months. Essentially this same process occurs in 

 the sexual reproduction of all plants and animals. 



Other algae found among pond scums. Great numbers of 

 different kinds of algae are found growing in fresh- water ponds 

 and pools, and when these are examined under the microscope 

 they are seen to be composed of the most beautiful and the 

 most varied cells found in the whole plant kingdom. Some 

 have intricate star-shaped and latticelike chloroplasts ; in 

 other forms the chloroplasts wind about within the cells like 

 spiral green ribbons. Some forms have no cell walls in the 

 filament, but all the living matter of the plant, with hun- 

 dreds of nuclei in it, lies together in one mass. A great group 

 of one-celled forms (Diatoms) have siliceous cell walls that 

 are like delicate cases of glass and that are sculptured and 

 marked with lines in a highly complex way. Some of these 

 forms are stationary, while others move slowly through the 

 water by invisible means. Still other forms swim about 



