About Green Leaves 197 



We have learned that the trees cannot make 

 starch without water. They need water, too, for 

 many purposes besides starch-making. 



Tiny leaves, just out of the bud, need a large 

 quantity to fill them out, and still more is required 

 to swell juicy berries and fruits. Dead leaves and 

 dried fruits weigh light because they have parted 

 with most of the water which they once contained. 



If the trees are to thrive they must get a num- 

 ber of mineral and chemical substances out of the 

 earth. There is but one way for these to enter 

 the body of the tree — through the root-hairs. 



But the root-hairs cannot take in this food from 

 the ground unless it is dissolved in water, and 

 earth-water holds but little mineral. A great 

 quantity of fluid must pass through the tree before 

 enough mineral substance can be separated out to 

 meet all the needs of summer growth and autumn 

 fruiting. 



This separation is not done until the water from 

 the earth gets into the leaves. 



Most of the foliage borne by native trees is 

 so made that moisture passes out of it quickly and 

 makes room for more earth-water coming up from 

 the roots. Leaves, broad and thin, spread them- 

 selves out to the light and air, as the laundress 

 spreads a sheet when she wishes it to dry quickly. 



Often the epidermis is so thin that water can 

 evaporate through it, and the leaves of all native 

 trees have their lower surfaces full of little pores, 



