Careless observation of Nature is responsible for some curious
misrepresentations of her most simple facts. Even those of us who
stand somewhat in the relation of nature teachers--namely, artists,
both draughtsmen and painters, and from whom we have a right to expect
absolute fidelity--are not free from our shortcomings as truthful
chroniclers. Thus how often we see otherwise beautiful landscapes
marred by features which rebel against all laws of natural
philosophy--of a storm sky above a sunlit scene, for instance, spanned
by the arc of the rainbow, and with all the shadows of trees and other
objects thrown sidewise! Then there is that inverted or very "dry"
crescent moon in western twilight skies; and how seldom do we see the
beautiful law of the twining tendril appreciated in the most careful
design of the botanical draughtsman!
For years the tendril was to me the conventional spiral, twisting like
a continuous curl or spring from the parent branch to the support
within its clasp; and it is safe to assert that not one in--well, a
good many of us, who should have gone out to our grape-vine or
passion-vine or melon-patch, without a previous forewarning, would
have been able to tell correctly the pretty little story of its
tendril methods, or have even noted the curious little kink which is
the infallible peculiarity of the climbing tendril.
What _is_ a tendril--botanically speaking? That depends. It is one
thing in this plant, quite another in that, so students of vegetable
anatomy or morphology soon discover.
It is soon perfectly plain that the stem is a modified root. For
instance, plants have been taken up from the sod and replaced in the
ground upsidedown, the roots subsequently becoming stems, and bearing
leaves, and the buried leafy stems assuming the functions of roots.
Leaves are mere modified branches, and the flowers modified leaves.
Pistils and stamens in flowers are modified petals, or rather petals
are modified stamens, the "doubling" of flowers representing the being
thus accomplished, while the petals again are mere changed leaves. A
neighbor of mine has a bush bearing green roses--all leaves. In the
water-lily you will find it difficult to determine just where the
stamen ends and the petals begin, so gradual is the blending. In the
peony the same is true, and carried still further in the merging of
petals and calyx into the approximate leaves.
And so it is with tendrils. In certain plants the point of the leaf,
through ages of "natural selection," has gradually been prolonged into
a slender arm, which clasps the branches of trees, and enables the
plant thus endowed to climb higher to sun and sky, and thus to thrive
more vigorously than its less fortunate brothers. The plant so
advantageously equipped transmits its tendency to its offspring, and
has therefore survived in place of its ancient fellows, and is the
type perpetuated or "selected" by nature. Such a tendril, then, is a
modified leaf. How is it in the pea? Here we find four leaflets in two
opposite pairs, but _no odd leaflet_ at the end of the main stalk,
such as we see in almost all other plants of its family. But in place
of this leaflet we find a branching tendril reaching out on all sides
for conquest. How quietly by the aid of these eager arms the sweet-pea
climbs to the top of its brush! In the common catbrier or smilax we
see two slender thread-like tendrils growing from the base of each
leaf. Here we have another modification, a development of the
"stipule," that tiny pointed growth common to many leaves, and
particularly notable at the base of a rose leaf. Still another plan
has been evolved in the grape-vine. If we examine our grape arbor in
June we find a number of drooping, swaying branches. The leaves are
scattered singly at intervals of a few inches along the branch, each
of the upper ones being attended on its opposite side by a drooping
cluster of mignonette-scented blossoms. Thus they follow down towards
the tip of the branch, where the clusters suddenly cease, and are
replaced by long, slender, curving and branched tendrils, sometimes
ten inches long. We might thus reasonably assume the tendril in this
case to be a modified blossom cluster, but there is no need for us
ever to assume such a thing. If we will only search with sufficient
care we shall at last discover the absolute proof of the fact in a
tendril which is partly in blossom, the nearest leaf-joint above it
having a full cluster of blossoms, and the tendril below it, nearer
the tip, not a few scattered flower-buds at its tips. This grape-vine
instance may be taken as a demonstration that in no case is the
tendril a special or primal organ, but merely an old one adapted to a
new purpose. In one instance from a leaf, in another from a
flower-stalk, just which can generally be determined by a sufficient
search for the telltale _intermediate form_ somewhere to be found on
the plant.
Among the most beautiful of all tendrils are those of the
passion-flower and plants of the melon family, notably the wild
star-cucumber, whose portrait is here presented. It is a more or less
common weed, to be found about gardens and barn-yards, where it covers
the fences with its profuse, clambering growth, its stalks everywhere
entangled or drawn close to support by their long, green, spiral
springs, and its free, branching, young tendril tips reaching out in
all directions for fresh foothold, and in its absence content at
length with a friendly intertwining among themselves, and a consequent
tangle of green convolutions. It is hard to believe that these long,
outreaching arms at the summit of this vine are identical with the
closely twisted spirals below, but such is the case; let any one of
them once feel the contact of even the frailest support of twig or
stalk, and it is soon close in the embrace of its eager tip, and the
contraction of the spring commences, but the method of this
contraction is worth our study.
In order for this tendril to coil it must _twist_, and it is perfectly
plain on general principles that with both ends held fast twisting is
impossible. But this little paradox is evidently dismissed by the
tendril. If we tie a short string between two given points, and
attempt to twist it with our finger and thumb, we succeed in turning
the string, 'tis true, but the twist on the right side neutralizes
that on the left, being in the opposite direction. In this way only
can the cord be twisted. If we twist with sufficient patience we may
imitate the coil of the tendril, which is performed precisely in this
way. Herein lies the secret of that little loop or kink in the centre
of all tendrils--a given point, which cannot be determined on the
extended tendril, but whose mission is to _reverse_ the twist in
opposite directions as soon as the tip has secured its contact, and
thus permit the coiling process to proceed. In tendrils of exceeding
length several of these reverse loops may be found at regular
intervals, sometimes as many as six in a single tendril, but the
coiling process usually awaits this contact. Unsatisfied tendrils of
the grape, for instance, will remain unchanged through the entire
season, or until their sensitive touch has been lost. Others, like
those of the passion-flower, will occasionally become discouraged and
curl up all by themselves, in which case, the other tip being free,
the curl is perfect and continuous and without the reverse loop, which
is now unnecessary. But the function of the tendril is to clasp and
hold. Its growth is not complete until thus quickened by the new
responsibility. Tendrils on duty become tough and sinewy in comparison
to their idling neighbors. How firm and rigid are these swollen coils
upon the grape-vine!
We do not gather "figs from thistles," but some equally incongruous
botanical associates are sometimes brought about through the
insinuating and clambering methods of the tendril. Have we not all
seen apple-trees bearing pumpkins or squashes or gourds, all
originally carried thither in the form of great yellow blossoms or
tender shoots! The grape-vine occasionally plays a singular botanical
prank in the orchard. Here is a drooping tendril which has been
swinging about for weeks from its vine canopy on the old apple-tree.
It had become almost discouraged, when a chance-favoring breeze wafted
its tip in contact with an apple close by. It was its last chance;
with its hooked extremity it clasped the stem of the fruit, and soon
made itself fast with three or four firm coils. Doubtless the little
reversing loop somewhere along the tendril was also awakened from its
chronic lethargy, and did its best to start the coil. Presumably it
succeeded, for the pull was sufficient to dislodge the apple, which,
falling to the entire length of the tendril, was still held fast in
the grip, whose new responsibility had given it new strength.
And there our apple hung for weeks, swinging like a pendulum from the
slender grape-vine, the coils on duty still keeping their firm grip on
the stem, even though all above were straightened by the weight of the
burden.