96 NATURE TEACHING 



in methylated spirit, and the colour obtained again on 

 once more putting them into iodine solution. Leaves 

 can thus be prepared in the summer and kept for use 

 as required during the winter. 



Take a leaf of a variegated geranium or other plant 

 with green and white leaves, which has been in a good 

 light for a day. Make a sketch of the leaf, shading in 

 the green parts. Decolorise the leaf by immersing in 

 boiling water and methylated spirit, and then place in 

 iodine solution. A pattern should be obtained similar 

 to the one drawn, showing that starch is formed only in 

 the green parts of the leaf, and that the white parts 

 contain no starch. Draw the leaf after treatment with 

 iodine, shading the blue parts, and compare it with your 

 previous sketch. 



The following experiment will serve to show that 

 unless a plant is provided with air no starch can be 

 formed in its leaves, even though it is placed in the light. 

 Germinate some peas and beans, and after the first 

 leaves have expanded, place the young plants in the 

 dark for a day. Test some for starch : if they contain 

 none, they are ready for use ; but if they still show the 

 presence of starch, replace them in the dark until they 

 are starch-free. Place some of the seedlings in bright 

 light in a window, giving water to their roots so that 

 they do not dry up. Put others in a thin glass vessel 

 full of water which has been boiled and allowed to cool 

 (this precaution is necessary to get rid of the air dissolved 

 in the water), and put these alongside the others in the 

 window. The plants should be weighted with small 

 stones to keep them well beneath the surface of the 



