100 MISSOURI STATE HORTICULTURAL SOCIETY 



the bark grows as fast as the wood under it, and needs no cutting. I 

 would therefore advise those who would keep their trees healthy to 

 let bark-splitting alone. 



THE LEAVES. 



The use of the leaves is but little understood even by our leading 

 horticulturists, while the great mass of farmers and gardeners never 

 even dream of the important work done by leaves. Tiiey are often 

 called the lungs of the plant; but since nearly the entire food of the 

 plant is drawn in and digested by them, they may with more propriety 

 be called the stomach. It is generally supposed that plants get most 

 of their nourishment from the soil, but this is a mistake; the food of 

 the plant is in the air, and the leaf is the organ to get it from the air 

 and prepare it for the plant. In all green leaves we find a substance 

 depending on iron for its formation. This green substance is called 

 chlorophyl, and occurs in grains, differing in this particular from other 

 coloring matters of plants which is held in solution by the sap. The 

 chlorophyl is the only substance that has the power to convert inor- 

 ganic matter into organic. It converts the carbonic acid of the air 

 that the leaves draw in through their mouths or stomata into starch, 

 which is the simplest organic compound known. Starch is composed 

 of carbon, oxygen and hydrogen, and forms in the leaves by the action 

 of the chlorophyl into grains that are made up by the addition of suc- 

 cessive layers. The oxygen and hydrogen may be obtained from wa- 

 ter, for this is composed of these two substances ; but the carbon is 

 not found in water nor in the soil, and hence must come from the air. 

 In traveling from the leaf to the other parts of the plant that it is to 

 feed, the starch has to pass through numerous membranes that show 

 no holes in them, even when viewed with the highest powers of the 

 microscope; this it is unable to do as starch, since this substance is 

 insoluble in water, and hence can not get through such membranes. 

 But starch differs but little from sugar in chemical composition; in fact, 

 sugar is starch with water added and a rearrangement of the atoms of 

 which the molecule is composed. We thus see that starch and sugar 

 are readily convertible one into the other. Now the sugar is soluble 

 in water and passes readily through membranes to all parts of the plant. 

 Most vegetable tissue has, besides the carbon, hydrogen and oxygen 

 of starch and sugar, a fourth element, nitrogen. Nitrogen is found in 

 the air, but it seems that plants are unable to obtain it from this source; 

 they must absorb it from the soil. Though the quantity of matter the 

 plant gets from the soil besides water is very small ; we must not infer 

 from this that it is of little importance. For instance, if the soil lacks 

 the small quantity of iron that enters into the composition of the chlo- 



