It grows out and not up. In other words a given section (horizontal) of an upright tree does not elongate. Professor Burrill declares that "It is quite impossible for a stem of a plant, after it aas become woody, to elougate by any process of growth." A contrary impression is sometimes given by the washing away of the earth about the roots, and it is declared to be possible for an entire tree to be raised slightly by the thiokening of the roots at the base of the trunk. The growth of all woods is by means of layirs, each one surrounding the preceding one, as the skin of a leek or onion does.