THE VARIOUS FORMS OF PLANTS 



147 



up by little bubbles of a gas which seems to arise from the body 

 of the plant. If we collect some of this uas. we can easily prove that 

 it is oxygen. The person who sees a pond with a covering of slimy 



-I, jar of water containing p<>n<l scum; B, same jar after an hour in the sunlight; 

 the pond scum lia.- risen to the top of the jar, buoyed up by the oxygen formed 

 within it. 



pond scum, knowing this fact, should no longer feel that the pond 

 is a menace to health, unless it is a place where mosquitoes live and 

 breed. 

 Under the low power of the microscope, the body of a pond scum 



Spirogyra : n, nucleus ; s, chlorophyll bands. 



is seen to be a thread made up of elongated cylindrical cells, each 

 of which contains a spirally wound band of chlorophyll within it, 



