INEQUILATERAL LEAVES .- BY PROFESSOR W. J. BEAL.

THE leaves of most plants, such as those of the white oak, sugar
maple, and tulip tree are equilateral, i. e., the right and left sides
are of the same size and match each other, as the two sides of the

Fig. 100.
Compound leaf. After Spencer.

nose and chin, or the right hand and foot match the left. Some
simple leaves and many leaflets of compound leaves show a marked

denomination of an "endopleura",-and an "albumen" besides, which contains the
embryo.
The true solitary seed-coat adhering to the pistil, the shrunken albumen will often be
found lying loose inside.
The contended fruit of the well-known yew-tree contains (1) an embryo, imbedded
within (2) an albumen, which is surrounded (3) by a tawny seed-coat. The latter loosely
adheres to a thickish capsule, which is itself covered by a thick, calycine layer !- in the
exact likeness of an acorn, a hazelnut, or the nut of the sweet gale (Myrica; the wax-
myrtle or bayberry) which indeed seems to reproduce the true (epigynous) structure of
the former on a reduced scale; as the (Composite) Polymnia Uvedalia or "nutted leaf-
cup."
The cup of the yew-tree thus remains to be properly interpreted as a fleshy cup
partly of dry scales, like those of the acorn and wax-myrtle on the one, and the succulent Euphorbia-involucres on the other hand.

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want of symmetry in their lobes. The Begonia is often cited as an
example. The hickory, bean and poison ivy, may illustrate the
same thing in compound leaves. In figure 100, "The homologous
parts a, b, c, d, while they are unlike one another, are, in their main
proportions, severally like the parts with which they are paired.
And here let us not overlook a characteristic which is less conspicuous but not less significant. Each of the lateral wings has winglets
that are larger on the one side than on the other; and in each case
the two sides are dissimilarly conditioned. Even in the several
components of each wing may be traced alike divergence from
symmetry, along with a like inequality in the relations to the rest;
the proximal half of each leaflet is habitually larger than the distal half." (Herbert Spencer, Principles of Biology, fig. 65, p.31.)

A. P. De Candolle says, "This inequality generally exists only
in alternate leaves, and I cannot find in my memoranda any example of an inequilateral opposite leaf. This fact tends to prove,
that this inequality ought to be referred to the position of the leaf
upon the plant favoring the development of one of its sides more
than the other; and in this case, it is always the lower one which
is developed most. This law is still more evident in the leaflets of
pinnate leaves .... the side most developed is always the lower,
the upper being narrower and less prolonged. The same observation may be made upon the stipules, which are very frequently irregular. In opposite leaves, there has been presented a curious example of inequality in Ruellia anisophylla;- one of two opposite
leaves is very small and narrow, and, as it were, abortive in comparison with the other; but symmetry is also met with in this irregularity, for on comparing the successive pairs, the small leaf is
found alternately on both sides. Stipules [sometimes] present
analogous phenomena."

Dr. Wilder has shown that "Elm leaves have the inner or upper side much larger," thus upsetting De Candolle's theory that the
inequality is due to the position of the leaf upon the stem. Various other reasons have been assigned for this inequality, all of
which seem to fail when applied to numerous examples in their
various stages of development.

Schleiden believes that this want of symmetry is due to unequal
pressure. in the bud. Spencer seems in doubt about the true
cause, for he says, "How far such differences are due to the positions of the parts in the bud; how far the respective spaces

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available for the parts when unfolded affect them; and how far
the parts are rendered unlike by unlikenesses in their relations to
light, it is difficult to say. Probably, these several factors operate in all varieties of proportion." He attributes the want of
symmetry in the leaves of the Lime tree or basswood to the shading of the smallest lobes. That this cannot be the case is proven
by an examination of the conduplicate leaves of the basswood and
elm while in the bud. When less than half an inch in length,
the lobes are plainly unequal. When much less than a fourth of
an inch long they are nearly or quite equal lobed. Since noticing
these facts, the writer was pleased to find the same views recorded
by Dr. Wilder.

On the basswood, the leaves are alternate and two ranked,
having the upper lobe fullest. This is the case even where the

Fig. 101.
Alternate two ranked leaves of Tilia Americana, Basswood, fullest at the base
on the inner side.

full lobe is shaded or where the whole leaf is well exposed to the
light. Spencer gives an illustration showing the arrangement of
basswood leaves, exposing nearly all their upper surface to the
light. If he should turn a young branch over, of this or almost
any other plant, he might be surprised to see how soon the leaves
would turn back again, and how nicely they would adapt themselves to each other, economizing all the available space. The
leaves of red elm and the American elm are sessile, broad at the
base, two ranked with the upper lobe fullest. The same is true of
the blue beech, Carpinus Americana, though the lobes are often
equilateral. Celtis occidentalis has two ranked leaves with petioles
half an inch long. The upper lobes of the leaves are very full
when compared with those of the elm. Begonia leaves arc two

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ranked with the upper lobe fullest, no matter whether they are
nearly sessile or on petioles a foot in length. The witch hazel has
two ranked leaves with
a broad base on short
petioles and the lower
lobe much the fuller.
The common beech,
hazel, mulberry, and
grape have two ranked,
equal lobed leaves.

Fig. 102.
Alternate two ranked leaves of Hamamelis Virginica, Witch Hazel, fullest at the base on the lower side.

It is a very common
thing to see a want of
symmetry in the lobes
of leaflets of compound
leaves. The reader
will remember that De Candolle says, "The upper edge of such is always smallest."

Fig. 103.
Two leaflets of Frarinus sambucifolia, Black Ash, fullest on the outer lobes.

Of this character, we find the black ash, the hop-tree (Plelea),
bean, hickory, elder, bladder-nut (Staphylea), strawberry, poison ivy, fragrant
sumach, and Jack in the
pulpit (Arisæma). The
ultimate divisions of the
decompound leaves of Hercules club are fullest on
the lower side, while the
leaves of the Kentucky coffee-tree reverse the above example. The
leaflets of Ailanthus are broad at the base, and raised on very short pedicels.

Fig. 104.
Two leaflets of Ailanthus glandulosus, fullest on the inner side.

 The upper edge of their leaflets is much the fuller.
Leaflets of the Southern prickly ash are fuller on the upper side,

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while those of the Northern prickly ash, of the same genus, are
usually fuller on the lower side. Rhus toxicodendron has the lower
edge of the side leaflets fuller; Rhus copalina has the upper edge
fuller. For some time, I thought as De Candolle wrote (though
I had not then read his book on the subject), that the unequal
lobed leaves were all alternate; and further, I thought they were
all two ranked along the stem, and thus set off against each
other, as leaflets in a compound leaf. 

Fig. 105.
Two opposite leaves of Euphorbia maculata, fullest on the lower side.

I was not much surprised, however, though much interested
to find that the opposite leaves of Cornus Florida
were fuller on the lower edge, as they were all
turned horizontally on the side branches. On the
4th of July, the two terminal leaves were about half
grown and generally equal lobed at the base, though
not always so. I find the opposite leaves of several
of our Euphorbias, as noticed in Gray's manual, are
fuller at the lower edge as they are turned down
horizontally. In a somewhat similar manner are
the two parts of the involucre of Carpinus Americana. These
stand with the fuller edge away from the axis. The two edges
of each are unequally serrate, more serrate on one edge than on
the other, so the involucral leaves match as well as the corresponding fingers on our two
hands. 

Fig. 106.
Involucre of Carpinus Americana, Blue Beech, the upper
or inner lobe narrower which grew next the axis.

In the greenhouse of the Michigan
State Agricultural College, is a plant unknown
to me, presented by Dr. Gray. The leaves are on
petioles three-fourths
of an inch in length; they are probably three ranked (certainly
not two ranked). As the leaves droop, the upper lobe is much
fullest and the midrib considerably curved as in Begonia.

So we have unequal lobed leaves on stems where they are two,
three or four ranked. The common sheep sorrel often has one
lobe longer and larger at the base, but I am unable to find any
rule with regard to this fact.

The four o'clock of our gardens Mirabilis has opposite leaves,
and when of proper size, terminates each axis with a flower.
The axillary bud on each side develops into a branch terminating

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in the same manner by a flower. Thus we have four leaves in two
pairs closely sitting about a flower. As thus arranged spreading
each way they are all fuller at the base on the side next the flower,
where there is least light and least room. This is contrary to
what we should expect according to De Candolle and Spencer.
An examination of the plant for a moment will make it clear.

Every botanist is familiar with the unsymmetrical petals on the
sides of the pea flower, violet, lobes of mint blossom, and those
of other plants.

The strangest thing under want of symmetry that I have seen
in plants, is found in the cotyledons of our cultivated buckwheat.

Fig. 107.
Cotyledons of Fagopyrum esculentum, Buckwheat,
each fullest on right lobe.

While in the seed, they are pressed together, and rolled up from
one edge. When the cotyledons have acquired
their full growth, they
have petioles about half
an inch long; each cotyledon is fullest on its left
side, so they would not
match each other without
turning one of them over.
Perhaps this is a puzzle
analogous to homologizing
the hand and foot on the
same side of the body.
All our theories so far
read or imagined, such as influence of heat, light, gravitation,
number of ranks on the stem, length of petiole, pressure, natural
selection, do not satisfactorily explain all these peculiarities.

So far, we agree with Dr. Wilder, "That such peculiarities are
true and original characteristics of the plants, and that they are
produced by the so-called vital force acting in a definite way."