THK FOOD OF PLANTS. 9o 



carbon dioxide should now be found, for, as 

 fast as it is formed by the breathing of the 

 plant, it is used up in the process of assimi- 

 lation. These three experiments teach us that 

 the processes of burning and the breathing of 

 animals and plants agree in resulting in the 

 formation of carbon dioxide. 



ft. Place some leaves in a wide-mouthed 

 bottle, fill with water, and place it in the 

 sunlight. Observe that in a short time small 

 bubbles of gas appear on the leaves, which are 

 in reality bubbles of oxygen, formed in the 

 process of assimilation and given off by the 

 plant. On repeating this experiment, but plac- 

 ing the bottle in the dark, no bubbles will 

 be given off, for, under these conditions, no 

 assimilation can go on. 



THE FOOD OF PLANTS. 



1. Take enough starch to just cover a 

 three-penny bit, drop it into about half a pint 

 of boiling water, and, when cold, add a little 

 iodine solution. The liquid becomes a deep 

 blue. (If you have too much starch present 

 the colour will be almost black and water 

 should be added). This is a convenient test 

 whereby to recognise the presence of starch. 



:>. Take a few leaves which have been 



