Green Leaves at Work 101 



the sun shines brightly upon a pool, in which 

 pond-weeds are growing lustily, we can see oxy- 

 gen rising in bubbles from the submerged leaf- 

 laboratories to the surface of the water. 



Oxygen-making is carried on even more actively 

 by the smallest of the fresh-water algae. These 

 little plants are fine green filaments, which have 

 no roots and float in tangled bunches near the 

 surface of still and sunny water. When the 

 weather is warm and bright, the oxygen given 

 out by these little algae forms great bubbles, 

 which become entangled in the cobwebby meshes 

 and float the plants to the surface. 



Here algae and bubbles together form a green 

 scum, which froths as we look at it. One might 

 readily suppose that all manner of impurities were 

 festering in the water, and that evil gases and 

 malaria were being distributed throughout the 

 neighborhood. But, as we learned in our copy- 

 book days, " appearances are deceitful." 



The frothing is caused by one of the most 

 active processes of constructive life. The bubbles 

 which are being cast up are life-giving oxygen, 

 which enables the grass to grow and the animal's 

 heart to beat. 



And the little algae, so busy and beneficent, 



