38 NEW ZEALAND NATURE-STUDY BOOK 
Formation of Starch in Leaves exposed to Sun- 
light. We have already seen that green leaves are able to 
absorb carbon-dioxide and form starch. This process can 
take place only in the presence of sunlight. The following 
experiment will verify this statement. 
Take a nasturtium or a sunflower leaf, pin a couple of 
pieces of cork on either side of it as shown, and expose it to 
sunlight for some time. Re- 
move the green colouring 
matter by first killing the 
leaf in boiling water and then 
placing it in methylated 
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hat the part from which the 
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mains bleached—whereas the 
rest of the leaf becomes bluish 
Fie gh Nesturtiumtentwith owing to the presence of 
starch. 
If the experiment is to be performed quickly—the plant 
should be kept in darkness for some days previous to being 
operated on. Otherwise the cork must be left on the 
plant for a few days before the starch test is applied. Tin- 
foil may be used instead of cork for covering up the whole 
or a portion of the leaf. Again, if a plant with variegated 
leaves be treated in the same way—we shall find that only 
in those parts which were originally green can starch be 
detected. The parts which were white will show no 
indication of starch. This is a further illustration of the 
fact that only the green parts of plants absorb carbon- 
dioxide and by its aid build up starch. 
How Plants grow towards the Light. That light 
is necessary for the growth of plants can be further 
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