10 
DIVERSITY OF LEAF FORMS. 
Eucalyptus leaves vary through such a wide range of forms that almost any 
statement about them must be taken with the understanding t at leie aie exc ]_ 
tions. The position in which a leaf is held will be modified by the shape and 
strength of its stalk or petiole and by the habit of the branchlets whether drooping 
or horizontal. The petiole of the balanced leaf is comparatively rigid, that of 
the vertical leaf flexible. A few species have long-stalked poplar-like leaves that 
sway and turn with the slightest breeze. Others have sessde or very short-s a m 
leaves that can move only with the twigs upon which they grow. Others, again, 
have leaves so narrow that, though they may be nearly equal-sided, the under sur¬ 
face cannot be shaded to a distinctly paler green. 
The hypothesis that the vertical or edgewise position of so many Eucalyptus 
leaves has been evolved by the necessity to economize moisture m a dry chmate 
is interesting, but we must not hastily accept it as if it were ascertained truth. 
There are great areas in Australia and Tasmania where there is and probably 
always has been a generous annual rainfall; and as we have seen, there are a goo 
many species whose leaves are not vertical. The immediate cause °f the vertica 
position is the pull of gravitation upon the unbalanced leaf-blade. This is obvi¬ 
ous from our knowledge of physical law. But if we ask what has caused so many 
species to produce unbalanced leaves, we raise a question the answer to which has 
still to be found. When Australian botanists have had time to pursue further 
their research upon this genus and its kindred genera over the whole range of their 
natural habitat, and when the palaeontologist has brought together larger numbers 
of ancestral fossil forms, the secret of the unbalanced leaf may become more clearly 
disclosed. This much is certain meantime that the eucalypts are what foresters 
call light demanders, and cannot reproduce themselves where the ground is heavily 
shaded. The distribution of their foliage in such manner that the light can pass 
through is therefore to their advantage by permitting seedlings to spring up and 
survive where otherwise reproduction would be impossible until the parent trees 
had fallen or died away. 
(d) BUDS, FLOWERS, AND FRUITS. 
BUDS AND FLOWERS. 
Eucalyptus trees produce their floral organs in small clusters or umbels. The 
number of buds, flowers, or fruits in each umbel is in many species normally three, 
in others seven; but in the majority of cases it is indefinite. A few species have 
numbers up to twenty or thirty or even more. The common stalk or peduncle of 
the umbel may be any length up to an inch or more. The stalklets or pedicels 
of the several flowers are usually shorter than the common stalk. In some cases 
the 1 flowers are quite without stalklets or sessile. As we have seen, the operculum 
or lid of the unopened floral bud, being always present and always undivided, 
serves as the distinguishing mark of the genus; by its shape and length it also 
helps us in separating one species from another. In some species it is hemispherical 
or like a dome; in others it is conical; in others, again, it is long and pointed like 
a horn. It may he round (terete) or angular, quite smooth or deeply ribbed or 
warty and rough. Its diameter may be anything from inch to f inch or more. 
When the operculum is long the stamens may be found packed in a bundle without 
bending or folding, like wheat in a sheaf; when it is short, as in the great majority 
of cases, the stamens will usually be found bent inwards or inflexed. 
