64 Fruit-growing in Arid Regions 



charcoal that is left when wood is so burned as to produce 

 this product. The air contains only three to four parts 

 of carbon dioxid in 10,000, so in order to make 1000 

 pounds of dry wood, 38,864,193 cubic feet of air must have 

 been taken into the plant. 1 



Stomata are found in green stems as well as in leaves, but 

 are usually more abundant on the under surface of leaves. 

 In order to do the enormous amount of work that leaves 

 are called on to perform, there must be great numbers 

 of these openings. The apple leaf, for example, contains 

 about 24,000 to the square inch. 2 



The next thing one notices in the diagram is that the leaf 

 is made up of a mass of irregularly shaped cells with air 

 spaces between them. These cells are largely occupied by 

 small, round, green bodies. This coloring matter, called 

 chlorophyll, is what gives the characteristic color to leaves. 

 It is in these minute bodies that the transformation of food 

 materials is performed. The green coloring matter ab- 

 sorbs energy from the sunlight, and the water from the soil 

 is combined with the carbon of the air to form sugar and 

 starch, and later, other combinations. The starch does 

 not remain here long, but is soon dissolved, transformed, 

 or combined, and passes through the sieve-tubes to parts 

 where food is needed or is stored in less active tissue when 

 an excess is made. 



At 3 is shown a leaf vein. Veins are largely made up 

 of a continuation of water vessels and of sieve-tubes. 

 It will be remembered that it is through the former that 

 the soil water passes up to the leaves, and the sieve-tubes 



1 Adapted from Strasburger, Noll, Schenck and Karsten, p. 215. 

 2 Bergen and Davis, "Principles of Botany," p. 104. 



