24 Common Trees 



This was one of the most interesting tree studies ever 

 undertaken by the writer of this handbook. He hopes that 

 many boys and girls will continue this study and help add 

 to our tree knowledge. 



T 



DO TREES BREATHE? 



HAT TREES BREATHE is a firmly established scientific fact. 

 _ Year after year, during night and day, in summer and 

 in winter, trees inhale oxygen and exhale carbon dioxide. 

 Trees breathe from the time they are seeds until they die. 



The leaves are often called the lungs of a tree. It is true 

 most of the oxygen enters through little openings on the 

 leaves. Most of these tiny openings are on the lower leaf 

 surfaces. They have been given the technical name of sto- 

 mata. On the leaves of some trees there have been counted 

 as many as 100,000 openings on a square inch. These little 

 doorways open to let in oxygen and to let out carbon diox- 

 ide. During the day trees also take in carbon dioxide and 

 give off oxygen through the small leaf openings. This is 

 a part of the process of food manufacture known under the 

 scientific name of photosynthesis. Not all the oxygen is 

 inhaled through the leaves, for some is taken in through little 

 openings on the twigs known as lenticels. They can read- 

 ily be recognized as pale to brown dots. On some trees, 

 such as the birches, cherries, and sumacs, they are large and 

 easily visible to the naked eye, while in other trees they arc 

 small and obscure. 



Trees also transpire, that is. give off water. We may call 

 it perspiring or "sweating." When an excess amount of 

 water is delivered to the leaves it is given off through small 

 stomata, the same openings through which the trees breathe. 

 This excess water is given off as an invisible vapor. Scientists 

 have estimated that a big oak may transpire as much as 150 

 gallons of water during a single day of summer. 



s 



HOW TO TELL THE AGE OF TREES 



OME TREES reach a great size and become very old, while 

 _ others remain small and die young. A definite age limit 

 cannot be set for each kind of tree, but for general use our 

 common trees may be said to be long-lived or short-lived. 

 Of our native trees, the White Oak, Button-wood, White 

 Pine, and Hemlock arc long-lived trees, and the Poplars, 

 Willows, some Cherries, and a few Oaks arc short-lived. 

 Some of the Sequoias of California exceed the 3,000-ycar 



