56 FtEST STUDIES IN PLANT LIFE 



the leaves that the sails do not need. This is sun- 

 light. 



9. Catching sunlight. Without the help of the 

 sun the leaf can get no food out of the air. Below 

 the thin skin on the upper side of the leaf there is a 

 soft, living green-stuff which, with the sun's help, 

 makes food for the plant. The carbon in the poison- 

 gas is kept for the plant's use, and the oxygen is 

 allowed to go into the air again. 



You will see, then, that the leaves take out of 

 the air a gas which is poisonous to us, and that they 

 return to the air a gas which is good for us.* We can 

 understand better now why our seedlings bent towards 

 the sun when we put them near a window. 



10. Experiments to shew that plants turn to the 

 sun. Grow some sunflower seedlings in the dark, 

 and you will find that though the growth is faster, it 

 is not a healthy growth. The long, weak, yellow 

 stems stretch out eagerly as if seeking for the sun. 

 The seed-leaves, too, can hardly open, and, when they 

 do open, are small. It is clear, then, that leaves are 

 made for the sun, and can do no good without it. 



11 Watch a healthy, young sunflower plant that 

 has reached its third pair of leaves. Observe these 

 leaves after dark, and see how they droop when theii- 



* It is important to note that this is only part of the truth. Plants, like 

 all other living things, breathe, that is consume oxygen, and give off caxbon 

 dioxide. This process during daylight is slight as compared with the 

 contrary process; but during the night the breathing of plants vitiates the 

 air in the same way as the breathing of animals. After the process of leaf- 

 feeding has been made clear, the process of leaf-breathing should be 

 explained. A plant feeds that it may work. In feeding it gives out oxygen ; 

 in working it destroys oxygen. To test this, place a handful of peas that 

 have been soaking for 24hours in a bottle. Corktightly. The germinating 

 peas will give off carbon dioxide. Prove by thrusting the lighted end of a 

 taper into the bottle. All this shows that plants should not be kept in 

 bedrooms. 



