36 Trees, Stars, and Birds 



Even in winter birch trees look quite different from ash 

 or hickory, not merely in color but in the appearance 

 of the branchlets. Can you explain the difference? 

 Name several trees with slender branchlets and others 

 with thick branchlets. 



The function of the branches is to hold the leaves up 

 to the light, and the number of branches required de- 

 pends on the size of the leaves. Trees with small leaves, 

 like birch, elm, and willow, have very numerous branch- 

 lets. Those with large leaves, like ash and hickory, 

 do not require so many branchlets. The leaves them- 

 selves reach out to the light and fill up the spaces in the 

 crown of the tree. Most palm trees, of which there are 

 a thousand kinds in the tropics, do' not branch at all, but 

 they have immense leaves with long stalks to reach out 

 to the light. 



Breathing pores in the bark of small branches. On 

 the twigs or small branches of a tree look for small ob- 

 long and elevated places on the bark. These are called 

 lenticels. They are breathing pores through which the 

 air can enter to reach the living inner portion of the 

 bark and from which water vapor escapes. On birch 

 and cherry trees the lenticels may be seen not only on 

 the branches but even on the trunk. Here they have 

 become elongated by the growth of the bark. Does 

 their long axis extend across the tree, or up and down? 



Lenticels are to be found on all trees. Where the 

 bark is very thick, as it is on old oaks, they are at the 

 bottom of the deep cracks. 



