STRUCTURE AND GROWTH OF THE PLANT. 25 



WORK OF THE LEAVES. The circulation of the sap brings 

 the water and material taken up from the soil to the leaf, 

 where also is found the carbon taken up from the air. And 

 it is in the green growing leaf that all this material is worked 

 over into such forms as the plant can make use of. The leaves, 

 we may say, are both the lungs of the plant and also the stom- 

 ach. If fire burns the leaves of a tree, or some blight or 

 disease attacks them, or insects devour them, the tree becomes 

 weak and in many cases soon dies. 



We observe the vitality of any plant in the leaves ; and we 

 should always try to keep the leaves fresh and free from attacks 

 of all kinds. The greenhouse gardener carefully washes the 

 leaves of his valuable plants, and the fruit-grower sprays his 

 trees and bushes for this purpose. When the leaves have 

 worked over all the food from the air and the soil (that is, 

 digested it, as we digest food in the stomach), it is carried 

 away in the sap to all parts of the plant to make root in one 

 place, more leaves in another, to increase the wood in the 

 branches, to form buds, or blossoms, or fruit ; in fact to build 

 up the plant in all its parts. How all this is done and no 

 mistake is made how leaves are formed in one place and 

 roots in another, and buds in another, is, as we have said 

 before, largely a mystery ; just as it is a mystery how hair 

 is formed on your head, teeth in your mouth, and nails upon 

 your fingers. 



We have another point to notice in regard to the leaves. 

 Cut off several long switches or branches from a willow, a 

 maple, an oak, a spruce, and currant bush. Observe how the 

 leaves are placed. They are not attached by chance. In 

 some cases two leaves grow out from the same part on 

 opposite sides. They are said to be opposite. In others there 

 is first one on one side and then the next above on the other 

 side. They are said to be alternate. Then, if you start with 



the first leaf and draw a line to the next, and then to the next, 



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