The work for the roots to do is to drink water. The upper half of the plant is very thirsty, and calls constantly for water. The roots push and dig into the moist soil, drink in water, and pass it up by a sort of pumping process. Only think, drinking and pumping! That is what roots do. And so if the earth is dry, and the roots can find nothing to drink, the plant will die. But after a shower see how glad the leaves seem, and how stiff and straight they stand, because the roots are sucking up great draughts of water.
To protect roots in their hard burrowing work a little cap of hard cells is fitted over their tips. Little hairs grow all over them, whose purpose is to help absorb moisture.
Some thick and fleshy roots are good to eat. They form many of our best vegetables. Beets, turnips, parsnips, and carrots are such roots. They belong to biennial or two-year plants. The first year they store up food in their roots; the second year draw upon this food, and produce flowers and fruit. They are named from their shapes. _Fusiform_, like radishes, when thicker in the middle, tapering at both ends. Carrots are _conical_, thicker at the top. Turnips bulge out in the middle, and are _napiform_. When clustered like a dahlia the roots are _fascicled_. All are _taproots_, or main roots. Besides these _primary_ roots there are _secondary_. You may have noticed secondary roots springing from the joints of a corn-stalk above ground. The wonderful banyan-tree sends down roots from its branches, making new trees, until one tree is the mother of a colony.
There are plants which take their nourishment from the air alone, and not from the soil. They need roots as hold-fasts, not as drinking-cups. Some lovely orchids grow in that way. Those leathery patches which you have seen on old fence-rails and rocks are lichens. They have roots for attachment only, and such are called _aerial_ roots.
Then there are _climbing_ rootlets. Look at the poison-ivy, but do not touch it, and you will see it climbing over tree-trunks and fence-posts by means of rootlets. The trumpet-creeper will show you the same thing. These rootlets are very strong, as you will find if you try to pull, as I did once, a trumpet-creeper out of a grape-vine.