Ftirthei' Growth and Duration of Plants. 33 



scar is healed by the cork. In oaks this cork is imperfectly 

 formed, so many of the leaves rustle all winter in the storm 



Fig. 38. — Apple stem. Section through (L) a lenticel (winter). (From Farmer's 

 " Practical Introduction to the Study of Botany.") 



until new buds formed in 

 their axils (the angle made 

 by the stem and the leaf) 

 push them off. 



To support and provide 

 food for the branches added 

 to the tree each year, the 

 stem must increase in thick- 

 ness. This it does by 

 means of a ring of active 

 cells just outside the woody 

 portion of the stem. These 



cells, the Cambium, are F'G. 39-— a. L^igitudinal section through the 



stem and base of the petiole of a poplar. 

 B- Part of the stem and petiole of A more 

 highly magnified. S, stem ; P, petiole ; I'.B. 

 vascular bundle ; C, cork tissue ; C.S. " sepa- 

 ration layer." (From Farmer's "Practical 

 Introduction to the Study of Botany.") 



most active in spring, when 

 their walls are so delicate 

 that they are easily broken. 



