314 



State Ilorticnlliiral Social v. 



passes to tlic leaves and young e^rowing- branches. Most of it passes off, 

 in tlic form of vapor from the leaves, but a part of it is used in building 

 up tlic substance of the tree. 



The ascending current of water rises through the zvood of the trunk. 

 (Fig. I.) The causes of the upward flow are not fully understood, but 

 in a general way it may be said to be accelerated by rapid evaporation 

 from tlie leaves. Therefore, more water will be given oil on a dry, windy 

 day than in moist, still weather. The water vapor passes out through 

 small pores in the epidermis of the leaves. Large trees undoubtedly give 

 ofT as much as thirty .to fifty gallons of water a day in dry weather. 



l^/A^£R 



iVAT£K 



T 



WATER AND 



iVATEfJ AND 

 SoLUtJLC SuBSTANCeS 



Fi?. 1. Diagram of the structure of a tree, sliowiug the path of the ascending and de- 

 scending currents. 



The advantage of this stream which enters the roots and passes out 

 through the leaves lies in the fact that it brings in dissolved minerals from 

 the soil and gives the plant a chance to use them in the manufacture of 

 new materials. 



Assimilation. — When wood is burned we see that a large part of it 

 is composed of carbon. The tree obtained this carbon from the carbon- 



