We eat as vegetables the fruits, or seed-vessels, of some plants; of others the root, the leaves, or some other part.

Vegetables, like fruits, contain base-forming acids and mineral matter of nutritive value. What salts are found in potatoes? Vegetables valued chiefly for this mineral matter may be eaten raw; to this class belong lettuce, celery, cucumbers, and all "salad plants." Many vegetables, however, require cooking. If we analyze one, we shall see why.