CHAPTER IV 

 LEAVES 



The leaves of a plant are always borne on the stem and have 

 the same relative position as the buds. (Figs. 20 and 21. ) They 

 are the expanded parts of the plant and have a definite rela- 

 tionship to the air and simlight. 



Green plants must have an expanded surface (usually the 

 foliage) into which the gaseous elements (Chapter X) of the 

 air may pass. These gaseous elements are as necessary for the 

 growth of the plant as are the raw food materials of the soil. 

 These expanded parts contain chlorophyll or the green coloring 

 material which is necessary for the formation of true food sub- 

 stances from the elements and compounds obtained from the 

 water, soil and air. 



Relation to Light. — If you stand under a tree and look 

 upwards, you will note that the leaves are on or near the tips of 

 the twigs and thus form a canopy or tent with the trunk and 

 branches as the supporting framework. If you place yourself 

 in such a position as to look down upon a small tree or other 

 plant or at a vine (Fig. 32), climbing over a wall you will be 

 surprised to note how very little the leaves shade one another, 

 and that all have very nearly the same light and air exposure. 

 The leaves of many plants, especially the legumes, are also 

 raised and lowered to some extent throughout the day in such 

 a manner as to receive the sunlight to the best advantage. 



The leaves are the factories in which the raw food sub- 

 stances are transformed into true food substances for the growth 

 of the plant. The water and these various raw or crude food 

 substances which may be dissolved in it are taken from the soil 



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