The Stourbridge Observer, Cradley Heath, Halesowen & District Chronicle.
Stourbridge, West Midlands, England, 1885-04-25 00:00:00

THE FORMS OF LEAVES.

Sir John Lubbock read a paper on this subject at
the last meeting of the Linnean Society, dwelling in
more detail on some points to which he had alluded
in a popular manner in his lecture at the Royal In-
stitution, and entering into some considerations which
time did not then permit him to discuss. He had
long been puzzled at the reason why some plants have
cordate leaves, more or less elongated, others palmate.
Starting from a foliaceous expansion of a stem, the
former was evidently the simpler type. It might be
considered as derived from a simple form, as for in-
stance the leaf of a grass. Such a leaf gradually
widened near the base would give the heart-shaped
form. He mentioned several plants which, although
when mature have palmate leaves, produce as seed-
lings one or more rounded ones, before developina the
final form. He had suggested that the cordate shape
was the earlier, from which the palmate was developed.
The interesting consequence would follow that if in
the same genus some species were cordate and others
palmate, the latter were of later origin. This expla-
nation presupposed that the palmate form, at any
rate under certain circumstances, presented greater
advantages. Sir John suggested that this might have
reference to the power of self-support and of resist-
ing wind. The weight of the leaf and the force of the
wind might be considered as if they were
concentrated on the central point of the
leaf. Now in palmate leaves the centre would be
nearer the point of support, and the resistance to
any given force, therefore, would be more
effectual. This point was illustrated by experi-
ment. Broad leaves, however, were of two main
types; cordate, with veins following the curvature of
the edge; and palmate or lobed leaves, with veins
running direct to the margin. Now, the fibres con-
stituting the so-called veins of leaves, contained
elongated cells running parallel to the veins. Con-
sequently the sap passing up the leaf-stalk and into
the leaves moved more readily along these fibrovas-
cular bundles, having fewer cell walls to traverse. It
was almost like going along a road instead of across
country. The fibrovascular bundles then acted as
pipes conveying the sap. and it is clearly more
economical that they should go straight to their
destination rather than wind in a curve. As the sap
passes more freely along the veins, the leaf also
grows there more rapidly, which seems to explain the
common-lobed form of leaf with a vein running to
the point of each lobe. Sir John Lubbock, with
reference to some criticism on hiso,views with
reference to the relation betweeni•the size of leaves
and the diameter of the stem, entered into certain
particulars, especially with reference to conifers,
pointing out that though the spruce fir, for instance,
had shorter leaves than the Scotch fir, while the stem
was as thick or thicker, yet the leaves remained on
much longer—say seven or eight years instead of two
or three. He also discussed various other interesting
problems presented by leaves—for instance, the pro-
bable reason for the larch having deciduous leaves,
and for the presence of two kinds of leaves on certain
cypresses and other trees.

"'lsn't my photograph excellent ?"said a young wife
To her husband. "Well, my dear," replied he, "I
fancy there is a little too much repose about the mouth
to be quite natural."
Lady: " Have you given the gold-fish fresh water, as I
told you, Maria ?" Maria: "No, ma'am; and why
would I? Sure, they haven't drunk what they have
vet 1"