90 



SOILS AND PLANT LIFE 



66. The Green Leaf likened to a Mill. — The process 

 may be likened to the work in a mill where com and oats, 

 we shall say, are ground together to make the " grist." 

 The water from the root corresponds to the corn ; the car- 

 bon dioxide from the air, to the oats ; the green leaf, to 



the mill; the sun- 

 light to the en- 

 gine; and the 

 starch formed, to 

 the grist. If any 

 part is lacking, 

 no grist can be 

 produced. 



EXERCISE 30 



Object. — To 

 learn how and 

 when food is man- 

 ufactured in the 

 leaves. 



Procedure. — 

 Place a few grains 

 of starch in a 

 saucer and cover with two or three teaspoonfuls of water. 

 Add a drop of tincture of iodine, and note that a blue-black 

 color appears. This is the test for the presence of starch. 

 Secure a potted plant, or use any growing plant in the 

 schoolyard. Provide several corks and pins, a small pan 

 of wood alcohol and some tincture of iodine. Place 

 slices of cork on opposite sides of a leaf and thrust a pin 

 through both to hold them snugly and firmly against the 

 leaf so that no sunlight can reach it where they are held 

 against its surface. The remainder of the leaf will be 

 exposed to the light. Prepare several leaves in this way. 



Fig. 29. — The green leaf as a mill. 



