94 NATURE TEACHING 



plunge them into boiling water for about two minutes, 

 and then place in strong methylated spirits. When the 

 liquid has become of a deep green colour owing to the 

 leaf-green being extracted pour it off and add fresh 

 spirit, repeating this until the leaves are free from colour. 

 Put one or two of these leaves in water containing a 

 small quantity of iodine solution ; they will turn blue. 

 The colour will not be a pure bright blue, but, owing to 

 the brown stain communicated to the tissues by the 

 iodine, of a somewhat greenish hue. 



Take a plant with smooth leaves for instance, a 

 fuchsia growing in a pot, and leave it exposed to the 

 sunlight from morning to afternoon. Then cut off one- 

 half only of two or three leaves, leaving the other halves 

 attached to the plant. Test the cut-off halves for starch 

 as described above. If they have plenty, place the 

 whole plant in the dark until the next day, either in a 

 cupboard or covered up by a box or tin, taking care 

 that no light at all gets in. Now cut off the remaining 

 halves of the leaves tested previously, and test these in 

 exactly the same way. If they have been in the dark 

 long enough (fuchsias usually require only twelve hours, 

 but some other plants take twenty-four hours or even 

 longer to get rid of all their starch) they will be found 

 to show no blue colour, indicating that all the starch 

 they contained has been used up during the time they 

 have been in the dark. 



Using the plant which we now know to have no 

 starch in its leaves, we can prove that starch is only 

 formed in the parts actually exposed to the light Take 

 some tinfoil or lead-paper (such as is used for tea pack- 



