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6 TREES 



air spaces, which communicate with the outside world by 

 the doorways mentioned above. An ordinary apple leaf 

 has about one hundred thousand of these stomates to each 

 square inch of its under surface. So the ventilation of the 

 leaf is provided for. 



The food of trees comes from two sources — ^the air and 

 the soil. Dry a stick of wood, and the water leaves it. 

 Bum it now, and ashes remain. The water aad the ashes 

 came from the soil. That which came from the air passed 

 off in gaseous form with the burning. Some elements from 

 the soil also were converted by the heat into gases, and 

 escaped by the chimneys. 



Take that same stick of wood, and, instead of burning it 

 in an open fireplace or stove, smother it in a pit and burn it 

 slowly, and it comes out a stick of charcoal, having its 

 shape and size and grain preserved. It is carbon, its only 

 impurity being a trace of ashes. What would have es~ 

 caped up a chimney as carbonic-acid gas is confined here as 

 a solid, and fire can yet liberate it. 



The vast amount of carbon which the body of a tree 

 contains came into its leaves as a gas, carbon dioxide. 

 The soil furnished various minerals, which were brought up 

 in the "crude sap." Most of these remain as ashes when 

 the wood is burned. Water comes from the soil. So the 

 fist of raw materials of tree food is complete, and the next 

 question is: How are they prepared for the tree's use.^^ 



The ascent of the sap from roots to leaves brings water 

 with mineral salts dissolved in it. Thus potassium, 

 calcium, magnesium, iron, sulphur, nitrogen, and phos- 

 phorus ai-e brought to the leaf laboratories — some are use- 

 ful, some useless. The stream of water contributes of 

 itself to the laboratory whatever the leaf cells demand to 



