The vascular tissue of higher plants has been an object of continuous
detailed study since the invention of the light microscope. As relevant
new physical, chemical and biochemical techniques and concepts have
appeared over the years, they have regularly and immediately been
applied to this field of enquiry. The reasons are not far to seek.
Vascular tissue provides the long-distance transport system for water
and nutrients within the plant, and an understanding of the structure
and development of the pathways within it is essential for an under-
standing of growth in all higher plants, including crop plants.
Moreover, parts of the vascular tissue - the whole of the xylem and the
fibers of the proble- have been, and still are, in high demand
commercially for their unique properties and as the only renewable
structural material on earth. There are, in addition, more subtle ways
in which xylogenesis, particularly as it allows the development of tree
species, contributes to the environment. A few years ago, while walking
in the foothills of the Pyrenees, I found all this expressed more
elegantly than I can express it, in a plea carved in wood at the
entrance to a forest: Homme!! Je suis la chaleur de ton foyer par les
froids nuits d'hiver, l'ombrage ami lorsque brule Ie soleil d'ete, l'eau
des rivieres et des sources. Je suis la charpente de ta maison, la
planche de ta table.