Abstract:
Of the four large subdivisions in the Vegetable Kingdom (each of which can be further divided into Classes, Orders, Families, Genera and Species) only two, the Pteridophytes and the Spermatophytes, can be classed as woody plants. The following are the principal characteristics which can be used to distinguish woody plants :-
(1) They are vascular plants - i.e., they possess a specialised conducting system consisting of xylem and phloem, the xylem being the wood of the mature plant.
(2) They are perennial plants - i.e., they live for a number of years - timber trees often for 200 years or more.
(3) They have a stem which persists from year to year, and in trees this is termed the bole or trunk.
(4) In addition, typical woody plants must have secondary thickening - i.e., they must have a means of thickening their stems by subsequent growth in diameter over a period of years. This is accomplished by a growing layer or Cambium situated between the last formed layer of wood (xylem) and the last formed layer of bark (phloem). This produces new wood and new bark in a layer between the older wood and older bark.
