We studied interspecific and ontogenetic relationships between
the size of a leaf and the primary diameter of the
internode bearing it. Although these two variables are known to be
strongly correlated across species, the form of
this relationship has not been studied. In a re-analysis of published
data on interspecific comparisons of 69
temperate tree species, we showed the existence of a strong relationship
between twig cross-sectional area (before
secondary growth) and surface area of leaves borne by it, within each
of three morphological groups, deciduous
angiosperms, evergreen angiosperms, and gymnosperms. Within each of
these groups, this relationship is
isometric: across species, primary cross-sectional area of the stem
increases proportionally with leaf surface area.
When we consider the relationship between the cross-sectional area of
a twig and the surface area of one leaf
borne by it, the y-intercepts for this relation are different for the
three groups. However, when total leaf surface
area per first-year shoot is considered, no differences remained
between gymnosperms and evergreen angiosperms,
but deciduous angiosperms continued to be distinct. This difference
between deciduous and evergreen groups
could be due to differences in leaf volume (evergreen species have
thicker leaves than deciduous) or in traits related
to a trade-off between life span of leaves and their physiological behaviour.
We present results of the first quantitative study of the relationship
between leaf size and primary diameter of
the stem during ontogeny. Both these parameters increase during
development of the plant from seedling to adult.
For the four tree species examined, the relationship between
primary cross-sectional area of the stem and leaf
surface area is also isometric.
These results bear on a functional interpretation of the
relationship between leaf and stem dimensions,
suggesting that vascular supply is directly proportional to the
requirements of leaves supported by the stem.