LIFE-HISTORY OF A TREE 69 



not visible to the naked eye, as they range in number from 

 800 to 150,000 to the square inch, varying with species. 

 The name stomata has been given them, and, as will be 

 seen, these little holes play an important part in producing 

 trees that will yield good lumber. Through them is admitted 

 air where it comes in contact, in the chlorophyl, with the 

 sap sent up by the roots and distributed throughout the 

 leaf by the numerous veins. In some way, through the ac- 

 tion of the chlorophyl, the carbonic acid gas which is min- 

 gled with the other gases of the atmosphere and named car- 

 bon-dioxide, combines with the mineral substance brought 

 up in the sap, and these inorganic substances are changed into 

 organic ones. They are, practically, digested and converted 

 into available food, which neither was before the combina- 

 tion took place. Just how this is done is not known, nor as 

 stated, is it fully understood in what manner, or through 

 what channels this prepared food is sent back from the 

 leaves through or along the stem and all the branches and 

 roots, leaving in their proper places in its passage such 

 particular food as goes to make wood, bark, leaves, buds, 

 flowers, and fruit. 



The Stomata as Breathing-Pores. In addition to ad- 

 mitting the air to the chlorophyl lying between the two 

 surfaces of the leaves, the stomata serve to let the excess 

 of water, which was necessary to carry the mineral food 

 from the roots to the leaves, evaporate and escape. This is 

 called respiration, and the amount of water some trees give 

 off when growing vigorously is astonishing. They also serve 

 to let the oxygen^ which has been rejected in the process of 

 preparinglEefood, escape, thus literally serving as breath- 

 ing-organs or mouths. The main difference^ between tree 

 and animal breathing is that the tree exhales the oxygen 

 and retains the carbon, while the animal rejects the carbon 

 and retains the oxygen. If the tree could not throw off the 

 oxygen, it would be practically smothered and would die, 

 while the same end would come to the animal if it could 

 not get rid of the carbon. 



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