FOLIAGE AS A LIGHT BARRIER 



This maple presents a mosaic of nearly continuous leaf surface exposed to the sun. 

 Inside its canopy of leaves, very little skylight filters through between leaves; and 

 we see that very little leaf surface is shaded from the light by other leaves 



young plant in a dark closet, we shall find after a few days that the tip has 

 been growing toward faint light coming through the keyhole. What 

 makes leaves face the light? Do they somehow "know" that light is neces- 

 sary for photosynthesis and so turn to it ? Do they like the light ? 



Water Changes Since roots absorb water (and mineral substances) 

 from the soil, the work they can do will depend upon moisture conditions. 

 Now we know that if there is relatively little water in the soil, roots will go 

 down deeper, into the moister layers of earth. From experiments we can 

 see that roots will change the direction of their growth according to the 

 side on which there is the greater humidity. 



Up and Down No matter which way seeds fall upon the ground, if 

 they sprout at all the stem grows upward and the root downward. If an 

 ordinary plant is placed in a horizontal position, the tip of the stem will 

 bend upward, and the root will bend downward. What makes the root 

 grow downward and the stem grow upward? These questions have been 

 fairly well answered by experiments conducted on many plants, in various 

 countries, over a long time. 



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