How a Tree Lives 73 



reason why it is not a wholesome plan to leave plants in 

 a sick person's room during the night, though during 

 the day they not only brighten the room but help to 

 keep the air pure. Water plants growing at the bottom 

 of streams get the carbonic acid gas they want out of the 

 water they grow in as there is always some dissolved in 

 it. If you watch a water plant in an aquarium in the 

 bright sunshine you will see a stream of little bubbles 

 coming up through the water. This is the oxygen which 

 the plant is setting free. 



You will want to know what becomes of the carbon 

 which trees are always collecting. Some of it is used to 

 make the wood of which the tree is built up. The black 

 substance which is left behind when you burn a twig or 

 a match is carbon or charcoal and shows you what a lot 

 there is in wood. Some more of the carbon is turned 

 by the leaves into starch and is stored up in the leaves 

 or roots to be used as food in the winter and spring when 

 the tree needs it. By using a certain stain which turns 

 starch blue you can see for yourself how a leaf that has 

 been in the sun is full of starch, while one that has been 

 in the dark for some hours has had to use up all its 

 starch as food and has not been able to make any more 

 because, as I have told you, the leaf cannot do its work 

 of collecting carbon in the dark. 



PRACTICAL WORK. 



1. (Demonstration.) Some peas which have been soaked for 

 24 hours are placed in a test-tube containing just enough water to 

 keep them moist. The test-tube is placed in a flask containing 

 a little lime water and fitted with a rubber cork. One end of a glass 

 tube passes through the cork into the flask, while the other forms 

 a U-shaped curve and is filled with coloured water. The, cork is 

 placed in the flask and the whole is made air-tight with vaseline. 



