All life and all that life accomplishes depend upon the supply of solar
energy stored in the form of food. The chief sources of this vital
energy are the fats and the sugars. The former contain two and a quarter
times the potential energy of the latter. Both, when completely
purified, consist of nothing but carbon, hydrogen and oxygen; elements
that are to be found freely everywhere in air and water. So when the
sunny southland exports fats and oils, starches and sugar, it is then
sending away nothing material but what comes back to it in the next
wind. What it is sending to the regions of more slanting sunshine is
merely some of the surplus of the radiant energy it has received so
abundantly, compacted for convenience into a portable and edible form.

In previous chapters I have dealt with some of the uses of cotton, its
employment for cloth, for paper, for artificial fibers, for explosives,
and for plastics. But I have ignored the thing that cotton is attached
to and for which, in the economy of nature, the fibers are formed; that
is, the seed. It is as though I had described the aeroplane and ignored
the aviator whom it was designed to carry. But in this neglect I am but
following the example of the human race, which for three thousand years
used the fiber but made no use of the seed except to plant the next
crop.

Just as mankind is now divided into the two great classes, the
wheat-eaters and the rice-eaters, so the ancient world was divided into
the wool-wearers and the cotton-wearers. The people of India wore
cotton; the Europeans wore wool. When the Greeks under Alexander fought
their way to the Far East they were surprised to find wool growing on
trees. Later travelers returning from Cathay told of the same marvel and
travelers who stayed at home and wrote about what they had not seen,