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This, of course, is the function that we are most interested in during a
discussion on transpiration. In most plants, the roots are responsible for
taking in water from the surrounding soil, along with the dissolved nutrients
that the water contains. Remember that these nutrients are not exactly "food"
for the plants; rather, they are the substances that the plant needs to
stay healthy so it can manufacture its own food by photosynthesis.
Plants have adapted different approaches for finding the water and nutrients
that they need.
Fibrous roots consist
of many relatively thin, highly branched, spreading roots. They intercept
water as it filters down through the soil, capturing the nutrients that
the water has picked up as it travels through the soil. Familiar plants
with fibrous roots include tomatoes and grasses.
Taproots, on the other
hand, consist of one or more large main root with smaller side roots.
These head deep into the soil to search for water and nutrients. Examples
of taproots include carrot and beet. Farmers and gardeners can use cover
crops of taprooted plants to "mine" nutrients from deep in the soil. As
the taproots take up these nutrients, they distribute them throughout
the plant body. When the mature plants are tilled into the soil, the nutrients
that they contain are incorporated into the topsoil-the region where most
crop plants' roots are concentrated.
Both fibrous roots and taproots have root hairs. These are very fine,
hairlike projections that occur in great numbers just behind the tip of
the growing roots. Roots take in water and nutrients by absorbing them
through their surface cells. The presence of root hairs vastly increases
the surface area available for this absorption.
Note how the presence of root hairs increases the area available for
absorption.
Roots as Anchors
Roots also have the enormous task of securing the plant in the
ground-through the wind and rain and snow and dark of night! Imagine
the force of a strong wind blowing through a huge tree, and you
can imagine the incredible strength of the roots keeping it upright.
A hurricane may take out hundreds of trees-but think of the thousands
still standing!
Roots have two different approaches to anchoring a plant. As we
mentioned before, fibrous roots tend to be concentrated near the
surface of the soil. These roots anchor the plant through an extensive
network of fine roots. Some plants have particularly extensive
root systems. For example, if all of the fibrous roots of a single
mature grass plant were laid end to end, they might stretch for
100 miles or more! Because of this characteristic, these plants
are usually good at controlling erosion.
Plants with taproots take a different approach. Taproots grow
straight down instead of spreading along the surface. These roots
can grow to great depths-some reach down 30 feet or more, anchoring
the tree securely in place.
Like stems, roots can become woody, providing strong anchors for
trees and shrubs.
Food Storage in Roots
Many plants store food in their roots. Perennial plants in
temperate climates must store enough food over the winter to
have the energy that they need to sprout in the spring. Because
of this food-storage function, many types of roots are filled
with  nutrients,
starches, and sugars.
We take advantage of this storage capacity when we grow and
consume root crops. Beets, carrots, parsnips, and radishes are
some of the roots-stored food-we enjoy.
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