CHAPTER II 



THE WORK OF THE LEAF 



The Increase of Weight in a Growing Plant is derived from the 

 Air. Plants split up Carbon Dioxide and give off Oxygen. 

 Purification of the Air by Plants. Formation of Starch in the 

 Green Leaf. Motive Power supplied by Light. All parts of 

 the Living Plant are also breathing. Necessity of Leaves to 

 the Growth and Ripening of the Plant. The Leaves of the 

 Plant give off Water. How much Rainfall is required by 

 Crops. 



The leaf is in many respects the most important part 

 of the plant ; it is essentially the manufacturing organ, 

 and on it depends the whole power of the plant to grow 

 — i.e, the fundamental process which produces fuel and 

 food for ourselves and the rest of the animal creation. 



As an understanding of the manner in which a leaf 

 works lies at the very foundation of our science, it will 

 be necessary to consider a number of experiments to 

 illustrate every phase of the action. 



In the first experiment weigh out a few grains of 

 mustard seed, and if you have not previously deter- 

 mined what percentage of water the mustard seed 

 contains, weigh out a second portion, and put this to 

 dry in the oven. Then take a pot filled with the 

 purest sand and mix some of the plant ash you have 

 previously made with the sand at the top of the 

 pot, add a suitable amount of water, and sow the 



19 



