Le 7 THE WORK OF PLANTS 
pale. Rinse the leaves for a moment in fresh water. 
Then place them in a tincture of iodine * made by dis- 
solving iodine crystals in alcohol. In afew moments the 
leaves become dark purple-brown in colour, sometimes 
nearly black, with a more or less blue or purplish tinge. 
This isthe colour given to starch when it takes up iodine. 
The experiment shows us that starch is present in the 
green leaves which have been for some time in the light. 
But if we should keep the plant in the dark for a 
day or two, and then test some of the leaves we should 
find no starch present. 
Where starch is formed in the 
variegated leaves of the coleus plant. 
The leaf of the coleus plant is 
variegated, that is, it has different 
colours. In this one which we are 
to study, part of the leaf is green 
and part 1s white, the green occupy- 
ing the middle portion and the bor- 

eee der, while the white forms a V 
IG. 148. Variegated leaf of 
7 2 eho pure between: We wish to know 
| which part of the leaf forms starch. 
We will immerse some of these variegated leaves in the 
strong solution of chloral hydrate overnight. Now they 
‘The tincture of iodine can be purchased at the drug store. Or 
one-quarter ounce of the crystals of iodine may be purchased and a few 
placed in alcohol as needed. 
