CHAPTER IV. 



LEAVES. 



INTRODUCTORY STATEMENT. 



Leaves are distinguishable into primary and secondary. The pri- 

 mary leaves arise directly from the first cells produced by the 

 division of the fertilized egg and in seed plants are called cotyle- 

 dons. They are usually transient, and not rarely are so distorted by 

 acting as storage places for reserve food that they do not function 

 as foliage leaves at all. The secondary leaves arise upon the sides 

 of the stem and are the ordinary foliage leaves of the plant. They 

 are very important organs in connection with the work of nutrition. 



PARTS OF A LEAF. 



In the typical foliage leaf there are three parts — the expanded 

 portion which is called blade or lamina, the leaf stalk (petiole), 

 and a pair of appendages at the base of the petiole known as 

 stipules. 



Fig. 443. Apple leaf; b, blade; p, petiole; s, stipules. 

 (After Thome.) 



