The total food value of vegetables, as well as of cereals, meats,
and, in fact, all foods, varies with the quantity of water and cellulose
they contain. Therefore, the vegetables that contain the least coarse
material are the ones that have the highest food value.
10. The green color that characterizes many vegetables is due to a
substance called _chlorophyl_. This substance is essential to the normal
growth of plants and is present in the correct amount in only those
which are properly exposed to the sunlight. Sufficient proof of this is
seen in the case of vegetables that form heads, as, for instance,
cabbage and head lettuce. As is well known, the outside leaves are
green, while the inside ones are practically white. Since it is exposure
to the light that produces the green color, a vegetable or plant of any
kind can be bleached by merely covering it in order to keep out the
sunlight. This procedure also enables the plants to remain more tender
than those which have been allowed to grow in the normal way and become
green. For instance, the inside leaves of a head of lettuce are always
very much more tender than the green outside leaves. In fact, the center
of any kind of plant, that is, the leaves and the stem that appear last,
are more tender, possess a lighter color, and have a more delicate
flavor than the older ones.
11. PROTEIN IN VEGETABLES.--Taken as a whole, vegetables are not high in
protein. Some of them contain practically none of this food substance
and others contain a comparatively large amount, but the average is
rather low.
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