LOW FORMS OF PLANT LIFE 



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along the coast is an alga. Some fresh-water algae are 

 the pond scums, which can be found on the water in 

 swamps and ponds. Some simple, one-celled algae can 

 be found on rocks and on the bark of trees. They give 

 to the rock and bark a greenish color. 



One pond scum is known as spirogyra, so-called because 

 of its spiral appearance under the microscope. It can be 

 found floating on the surface of 

 the water in masses composed of 

 hair-like threads with bubbles 

 of gas distributed through it. 

 This gas, composed mostly of 

 oxygen, causes the spirogyra to 

 float. It grows by using the 

 impurities in the water and the 

 carbon dioxide of the air. When 

 starch is being made, there is 

 an excess of oxygen gas which is 

 given off and forms the bubbles 

 which hold the plant on the 

 surface where it can get more sunlight and air. This, 

 plant is useful in so far as it lives on the impurities in 

 the water and gives off oxygen to the air. It is harmful 

 to the extent that it gets into drinking water and gives 

 it a peculiar odor and taste. 



A thread of spirogyra is made up of a single row of 

 cells attached end to end. A thread increases in length 

 by the cells dividing one cell becoming two cells, the 

 ends remaining fixed to each other. 



Spirogyra does not bloom and grow seed like the higher 

 plants, but, when a time that is unfavorable for growth 

 comes, it produces a cell that corresponds to a seed. This 

 cell is known as a spore, sometimes called zygospore. It 



SPIROGYRA A POND SCUM 

 A is one cell; B is two spore 



cells formed by the union 



of two other cells. 



