CHAPTER TWO 



LEAVES AND THEIR STRUCTURES 



The leaves of plants are their most conspicuous part. The 

 summer landscape owes its color to them ; and even when we 

 look at a near-by plant, the 

 leaves attract most of our 

 attention and the plant stem, 

 like the staff of a flag, is likely 

 to be overlooked. The promi- 

 nence of leaves is not the result 

 of chance, for leaves manufac- 

 ture food and sunlight is neces- 

 sary for this process. In this 

 chapter we shall study the 

 structure of a leaf, and in sub- 

 sequent chapters we shall dis- 

 cuss the work of the leaves and 

 the processes that take place 

 within these important organs 

 of the plant. 



The parts of a leaf. If we 

 examine a leaf closely, w^e see 

 that it consists of a broad, thin blade, marked into small 

 divisions by veins. The vein near the middle of the blade is 

 commonly larger than the others and is called the midrib. 

 In some forms of leaves there are several prominent veins, 

 which we may call the principal veins. In general, the small- 

 est veins form a network uniting with the larger ones, and 

 these in turn connect with the midrib or with the principal 

 veins. These large veins are smallest at the apex or outer 

 end of the leaf, and gradually become larger toward the base 



13 



Fig. 6. Leaf of tulip tree, showing 

 parts of a complete leaf. 



