paper. The negative is taken
on one film, then this is printed on another film. The second film is
"right side out."

LIGHT AND THE MANUFACTURE OF FOOD IN PLANTS. Much the most important
chemical effect of light, however, is not in making photographs, in
bleaching things, or in "burning" your skin. It is in the putting
together of carbon and water to make sugar in plants. Plants get water
(H_2O) from the earth and carbon dioxid (CO_2) from the air. When
the sun shines on chlorophyll, the green substance in plants, the
chlorophyll puts them together and makes sugar. The plant changes this
sugar into starch and other foods, and into the tissues of the plant
itself. Nothing in the world can put carbon dioxid and water together
and make food out of them except certain bacteria and the chlorophyll
of plants. And light is absolutely necessary for this chemical action.
Try this experiment:

EXPERIMENT 102. Pin together two pieces of cork on opposite
sides of a leaf that is exposed to the sun. The next day take
this leaf from the plant and heat it in a beaker of alcohol
until the green coloring matter is removed from the leaf. Then
place the leaf in a glass of water that contains iodine.
The iodine will color the leaf dark where the cells contain
starch. (See Experiment 115, page 373.) Is starch formed where
the light does not reach the leaf?

No plant can make food except with the help of light. The part of the
plant that can put carbon dioxid and water together is the green stuff
or chlorophyll, and this can work only when light is shining on it. So
all plants would die without light.

But if all plants should die, all animals would die also, for animals
cannot make food out of carbon dioxid and water, as they do not have
the chlorophyll that puts these things together. A lion does not live
on leaves, it is true, but he lives on deer and other animals that
do live on leaves and plants. If the plants died, all plant-eating
animals would die. Then there would be nothing for the flesh-eating
animals to eat except each other, and in time no animals would be left
in the world. The same thing would happen to the fish. And man, of
course, could no longer exist. The food supply of the world depends on
the fact that light can start chemical change.

OXYGEN RELEASED IN THE MANUFACTURE OF PLANT FOOD. Besides in one way
or another giving us all of our food, plants, helped by light, also
give us mos