1059. 'The functions of the root are to fix plants in the earth, and to absorb nutriment from it' (Lindl.) Boots lengthen by forming additional cellular tissue at their extremities; and they possess the power of selecting, from the matter presented to them, the food that is best suited to their wants; and when that food is not easily to be obtained, they will elongate themselves in an extraordinary manner in search of it. The modern theory for explaining the rotation of crops is, that plants exhaust the soil of certain mineral substances which are necessary for them; but that as different minerals are wanted by different plants, the same soil which has become quite unfit for growing one kind of plant, may be perfectly suitable for another.
