9 
SAPLING AND ADULT LEAVES. 
carry leaves considerably larger than those of the adult tree. The colouring of 
their young foliage is often very rich and beautiful. Upon close scrutiny we shall 
find that in their hues and in the sheen of their leaves they show differences that 
may well be noted when we are endeavouring to ascertain their place among the 
species. 
LEAVES OF TEIE ADULT TREE. 
Adult tree leaves vary so greatly amongst the numerous species in size, shape, 
texture, thickness, and colouring that it is impossible to include them all in any 
one descriptive formula; but certain general statements may be made about them 
that will help us very much when we come to the definition of individual species. 
In all Eucalyptus leaves the intramarginal veins characteristic of the Myrtaceae 
are obviously present, and can be traced nearer to or more remote from the edges 
of the leaf. The oil glands that are the source of the strong odours emitted when 
the leaves are crushed or exposed to heat are also always present in larger or 
smaller numbers. The main lateral veins spring from the midrib at angles vary¬ 
ing in the different species and terminate in the intramarginal vein. 
In one great group of species the lateral veins go off at angles that are not 
very acute and form nearly parallel lines in the leaf somewhat like the lateral parts 
of a feather. Such leaves are sometimes spoken of as feather-veined. With this 
venation we often find a form of leaf in which the two sides are equal or nearly 
equal and the midrib approximately in alignment with the leaf-stem or petiole. 
The leaf in this case is balanced and presents its upper surface to the light, the 
under surface being shaded and consequently of paler green and less shiny. 
But we also find in this balanced-leaf group a very large percentage of leaves 
that are not equal-sided. We even find in it leaves that are strongly curved to 
one side. In these cases the leaf-blade maintains its balance by a compensating 
bend or twist in the petiole, and thus still presents its upper surface mainly to the 
light. 
In another great group of species we find a more acute venation and asso¬ 
ciated with it a form of leaf in which the two sides are always very unequal. The 
stronger development of the leaf on the one side forces the midrib into a curve in 
the opposite direction and out of alignment with the petiole. The leaf-blade 
becomes falcate or scythe-shaped. Such a leaf is over-weighted on the arched or 
concave side and gradually falls into a vertical position with a half twist in the 
petiole. The two surfaces are equally exposed to the light, and as the result are 
of about the same shade of green. 
Stated a little more technically, the meaning of the words balanced and 
unbalanced as applied to petiolate leaves is as follows:— (a) When a petiolate 
leaf is so formed that a straight line drawn centrally through its petiole and 
produced through its blade would cut the blade into two parts equal in weight the 
leaf is balanced, no matter what may otherwise be its shape. Such a leaf will dip 
less or more towards its free end, but will continue to present its uppei sui face 
mainly to the light. ( b ) When a petiolate leaf is so formed that a straight line 
drawn centrally through its petiole and produced through the blade would cut the 
blade into two parts unequal in weight the leaf is unbalanced, no matter what 
may otherwise be its shape. Such a leaf will not only dip less or more towards its 
free end, but will at the same time turn to an edgewise position and present its 
two surfaces about equally to the light. 
