HOW PLANTS GET FOOD FROM SOIL AND AIR 37 



the center of the tree top. In which position would they receive most 

 light? 



NOTE TO THE TEACHER. OPTIONAL EXERCISE. Tincture of iodine 

 makes starch change to a purple color. Add a few drops of this to 

 a teaspoonful of water ; with this moisten a thin slice of Irish potato, 

 sweet potato, bread, cut corn grain, plant stems, or lettuce leaves. 

 Before staining green leaves with iodine you should dissolve out the 

 leaf green with alcohol very carefully heated in a vessel of hot water. 

 A substance not colored purple by iodine solution lacks starch. Test 

 a slice of meat ; a cut stem of whitened grass from under a board ; the 

 white inner leaves of cabbage ; or the white or white-variegated leaves 

 of coleus, etc. ; and any leaf that has been kept in darkness for several 

 days. 



FIG. 29. A FERN THAT SUFFERS 

 FROM TOO LITTLE SUNLIGHT, 

 SHOWING POOR FOLIAGE AND 

 GROWTH 



