that some tendrils have originated from modified leaves, and others
from modified flower-peduncles; so that some are foliar and some
axial in their homological nature. Hence it might have been expected
that they would have presented some difference in function. This is
not the case. On the contrary, they present the most perfect identity
in their several remarkable characteristics. Tendrils of both kinds
spontaneously revolve at about the same rate. Both, when touched,
bend quickly to the touched side, and afterward recover themselves
and are able to act again. In both the sensitiveness is either
confined to one side or extends all round the tendril. They are
either attracted or repelled by the light. The tips of the tendrils
in these two plants become, after contact, enlarged into disks, which
are at first adhesive by the secretion of some cement. Tendrils of
both kinds, soon after grasping a support, contract spirally; they
then increase greatly in thickness and strength. When we add to these
several points of identity the fact of the petiole of the Solanum
jaspinoides assuming the most characteristic feature of the axis,
namely, a closed ring of woody vessels, we can hardly avoid asking
whether the difference between foliar and axial organs can be of so
fundamental a nature as is generally supposed to be the case.
We have attempted to trace some of the stages in the genesis of
climbing plants. But, during the endless fluctuations in the
conditions of life to which all organic beings have been exposed, it
might have been expected that some climbing plants would have lost
the habit of climbing. In the cases of certain South African plants
belonging to great twining families, which in certain districts
of their native country never twine, but resume this habit when
cultivated in England, we have a case in point. In the leaf-climbing
Clematis flammula, and in the tendril-bearing vine, we see no loss
in the power of climbing, but only a remnant of that revolving power
which is indispensable to all twiners, and is so common, as well as
so advantageous, to most climbers. In Tecoma radicans, one of the
Bignoniaceæ, we see a last and doubtful trace of the revolving power.
With respect to the abortion of tendrils, certain cultivated
varieties of Cucurbita pepo have, according to Naudin, either quite
lost these organs or bear semi-monstrous representatives of them.
In my limited experience I have met with only one instance of their
natural suppression, namely, in the common bean. All the other
species of Vicia, I believe, bear tendrils; but the bean is stiff
enough to support its own stem, and in this species, at the end of
the petiole where a tendril ought to have arisen, a small pointed
filament is always present, about a third of an inch in length, and
which must be considered as the rudiment of a tendril. This may be
the more safely inferred, because I have seen in young, unhealthy
specimens of true tendril-bearing plants similar rudiments. In the
bean these filaments are variable in shape, as is so frequently
the case with all rudimentary organs, being either cylindrical or
foliaceous, or deeply furrowed on the upper surface. It is a rather
curious little fact that many of these filaments when foliaceous
have dark-colored glands on their lower surfaces, like those on the
stipules, which secrete a sweet fluid; so that these rudiments have
been feebly utilized.
One other analogous case, though hypothetical, is worth giving.
Nearly all the species of Lathyrus possess tendrils; but L. nissolia
is destitute of them. This plant has leaves which must have struck
every one who has noticed them with surprise, for they are quite
unlike those of all common papilionaceous plants, and resemble those
of a grass. In L. aphaca the tendril, which is not highly developed
(for it is unbranched, and has no spontaneous revolving power),
replaces the leaves, the latter in function being replaced by the
large stipules. Now, if we suppose the tendrils of L. aphaca to
become flattened and foliaceous, like the little rudimentary tendrils
of the bean, and the large stipules, not being any longer wanted, to
become at the same time reduced in size, we should have the exact
counterpart of L. nissolia, and its curious leaves are at once
rendered intelligible to us.
It may be added, as it will serve to sum up the foregoing views on
the origin of tendril-bearing plants, that if these views be correct,
L. nissolia must be descended from a primordial spirally twining
plant; that this became a leaf-climber; that first part of the
leaf and then the whole leaf became converted into a tendril, with
the stipules by compensation greatly increased in size; that this
tendril lost its branches and became simple, then lost its revolving
power (in which state it would resemble the tendril of the existing
L. aphaca), and afterward losing its prehensile power and becoming
foliaceous would no longer be called a tendril. In this last stage
(that of the existing L. nissolia) the former tendril would reassume
its original function as a leaf, and its lately largely developed
stipules, being no longer wanted, would decrease in size. If it be
true that species become modified in the course of ages, we may
conclude that L. nissolia is the result of a long series of changes,
in some degree like those just traced.
The most interesting point in the natural history of climbing plants
is their diverse power of movement; and this led one on to their
study. The most different organs--the stem, flower-peduncle, petiole,
midribs of the leaf or leaflets, and apparently aerial roots--all
possess this power.
In the first place, the tendrils place themselves in the proper
position for action, standing, for instance, in the Cobæa, vertically
upward, with their branches divergent and their hooks turned outward,
and with the young terminal shoot thrown on one side; or, as in
Clematis, the young leaves temporarily curve themselves downward, so
as to serve as grapnels.
Secondly, if the young shoot of a twining plant, or of a tendril,
be placed in an inclined position, it soon bends upward, though
completely secluded from the light. The guiding stimulus to this
movement is no doubt the attraction of gravity, as Andrew Knight
showed to be the case with germinating plants. If a succulent shoot
of almost any plant be placed in an inclined position in a glass of
water in the dark, the extremity will, in a few hours, bend upward;
and if the position of the shoot be then reversed, the now downward
bent shoot will reverse its curvature; but if the stolon of a
strawberry, which has no tendency to grow upward, be thus treated, it
will curve downward in the direction of, instead of in opposition to,
the force of gravity. As with the strawberry, so it is generally with
the twining shoots of the Hibbertia dentata, which climbs laterally
from bush to bush; for these shoots, when bent downward, show little
and sometimes no tendency to curve upward.
Thirdly, climbing plants, like other plants, bend toward the light
by a movement closely analogous to that incurvation which causes
them to revolve. This similarity in the nature of the movement was
well seen when plants were kept in a room, and their first movements
in the morning toward the light and their subsequent revolving
movements were traced on a bell glass. The movement of a revolving
shoot, and in some cases of a tendril, is retarded or accelerated
in traveling from or to the light. In a few instances tendrils bend
in a conspicuous manner toward the dark. Many authors speak as if
the movement of a plant toward the light was as directly the result
of the evaporation or of the oxygenation of the sap in the stem, as
the elongation of a bar of iron from an increase in its temperature.
But, seeing that tendrils are either attracted to or repelled by the
light, it is more probable that their movements are only guided and
stimulated by its action in the same manner as they are guided by the
force of attraction toward the centre of gravity.
Fourthly, we have in stems, petioles, flower-peduncles and
tendrils the spontaneous revolving movement which depends on no
outward stimulus, but is contingent on the youth of the part and
on its vigorous health, which again, of course, depends on proper
temperature and the other conditions of life. This is, perhaps, the
most interesting of all the movements of climbing plants because it
is continuous. Very many other plants exhibit spontaneous movements,
but they generally occur only once during the life of a plant, as in
the movements of the stamens and pistils, etc., or at intervals of
time, as in the so-called sleep of plants.
Fifthly, we have in the tendrils, whatever their homological nature
may be, in the petioles and tips of the leaves of leaf-climbers,
in the stem in one case and apparently in the aerial roots of the
vanilla, movements--often rapid movements--from contact with any
body. Extremely slight pressure suffices to cause the movement. These
several organs, after bending from a touch, become straight again,
and again bend when touched.
Sixthly, and lastly, most tendrils, soon after clasping a support,
but not after a mere temporary curvature, contract spirally. The
stimulus from the act of clasping some object seems to travel slowly
down the whole length of the tendril. Many tendrils, moreover,
ultimately contract spontaneously even if they have caught no object;
but this latter useless movement occurs only after a considerable
lapse of time.
We have seen how diversified are the movements of climbing plants.
These plants are numerous enough to form a conspicuous feature in
the vegetable kingdom; every one has heard that this is the case in
tropical forests; but even in the thickets of our temperate regions
the number of kinds and of individual plants is considerable, as
will be found by counting them. They belong to many and widely
different orders. To gain some crude idea of their distribution in
the vegetable series, I marked from the lists given by Mohl and Palm
(adding a few myself, and a competent botanist, no doubt, could add
many more) all those families in _Lindley’s Vegetable Kingdom_,
which include plants in any of our several subdivisions of twiners,
leaf-climbers, and tendril-bearers; and these (at least some of each
group) all have the power of spontaneously revolving. Lindley divides
Phanerogamic plants into fifty-nine alliances; of these, no less than
above half, namely, thirty-five, include climbing plants according to
the above definition, hook and root-climbers being excluded. To these
a few Cryptogamic plants must be added which climb by revolving. When
we reflect on this wide serial distribution of plants having this
power, and when we know that in some of the largest, well-defined
orders, such as the Compositæ, Rubiaceæ, Scrophulariaceæ, Liliaceæ,
etc., two or three genera alone, out of the host of genera in each,
have this power, the conclusion is forced on our minds that the
capacity of acquiring the revolving power on which most climbers
depend is inherent though undeveloped in most every plant in the
vegetable kingdom.
FLOWER COLORATION
--ALEXANDER S. WILSON
The Prophet-plant (Arnebia echioides) is a native of Persia and
Arabia, but has been introduced and grows freely in gardens in
England. Its chief interest lies in its variable flowers, which may
fairly rank with those of the changeable Hibiscus and other
“Plants divine and strange
That every hour their blossoms change.”
The plant is about two feet in height, and somewhat resembles a
cowslip or an auricula. It belongs to the natural order Boraginaceæ,
and is nearly allied to the lungwort, viper’s-bugloss, borage, and
forget-me-not, all of which exhibit color changes more or less
distinct. The various species of Myosotis, or forget-me-not, are
also called scorpion grasses, from the upper flower-bearing portion
of the stem being curled on itself like a watch-spring. The cluster
of flowers, forming the inflorescence of Arnebia, develops in same
scorpioid fashion. There is a double row of flower buds on the
curled stalk, and as this gradually unwinds pair after pair of the
flowers expand in succession. In shape and color the individual
flowers are not unlike those of the primrose, though rather smaller.
When a flower first opens, five conspicuous jet-black spots are seen
upon the yellow rim of the salver-shaped corolla. If the flower be
examined the following day, we are surprised to discover that the
black spots have vanished as if by magic. The yellow of the corolla
is also much paler, and a little later on presents quite a bleached
and silvery appearance, the petals becoming almost white. No sooner
have the spots disappeared from the first pair of flowers than a
second pair expand, and display their sable marks in bold relief
upon the yellow enamel of their petals. From this time onward the
inflorescence comprises both kinds of flower, those but newly opened
having the five conspicuous spots, and the older ones on which no
spots are visible. From these dark spots--the so-called finger-marks
of Mahomet, Arnebia has received its name--the Prophet-plant. Its
flowers seem bewitched, the change is so pronounced and obvious; a
day or two after unfolding they differ so much from the newly opened
ones beside them, that were they growing on separate plants, we
should at once set them down as belonging to another species.
This change of color gives rise to another interesting peculiarity.
If Arnebia be examined by daylight, and again in the dim twilight,
the observer is struck by a remarkable circumstance. In broad
daylight, the golden spotted flowers at once arrest the eye, while
their paler companions are hardly observed. The inflorescence owes
by far the greater part of its display to the younger flowers. In
the dusk this is entirely reversed; the conspicuousness of the
inflorescence now depends on the paler flowers, and the others are so
obscured that a second glance is needed before they can be discerned.
The relative brilliancy of the two sets of flowers can also be tested
by gradually retiring from the plant, keeping the eyes still fixed
on the blossoms. At dusk the young flowers are lost sight of much
sooner than the others; by day the older ones first disappear in the
distance. This peculiar transformation imparts to the inflorescence
of Arnebia a faint similitude of the pillar of cloud by day and
of fire by night--that celestial manifestation of sacred story so
closely associated with the native region of this desert flower.
Here, then, we have one of those phenomena which for the naturalist
possess all the fascination of a mystery. What can be the explanation
of this remarkable change of color, and what advantage does the
flower derive from the sudden disappearance of its spots and the
blanching of its petals?
With the reader’s permission, we shall now proceed to show why nature
has bestowed on Arnebia what she has denied to the leopard--the
power of changing its spots. Before we can say why any flower
should change its color, we must first know why a flower is colored
at all, and why all flowers are not colored alike. Almost all the
peculiarities of flowers can be explained as having reference to
the visits of insects. The honey is secreted as an inducement,
while the secret and brilliant colors serve to attract the
attention of the honey-gatherers. The researches of the late Charles
Darwin demonstrated the importance of cross-fertilization in the
vegetable kingdom. Very many flowers are quite sterile with their
own pollen; in other cases, although the flower has the capacity of
self-fertilization, the resulting seeds are of very inferior quality
compared with those obtained as a result of cross-fertilization. As
carriers of pollen, then, insects perform an essential service to
plants, and it is in order to secure their services that flowers are
brightly colored.
For the variety of color observed among flowers there appear to be
two principal reasons. A little reflection will show that, since
flowers are so dependent on insects for the conveyance of their
pollen, it must be to the advantage of each species of plant to
possess flowers distinctively colored and capable of being easily
recognized by honey-seeking insects. A bee does not visit all flowers
indiscriminately; it would be greatly to the flowers’ disadvantage if
it did. In the course of a single journey the bee for the most part
restricts itself to the flowers of one species, and has been known
to visit as many as thirty dead-nettles in succession, passing over
all other flowers. Time is saved by this method, for by keeping to
one kind of flower at a time the insect becomes familiar with its
outs and ins, and the practice thus acquired enables it to overtake
a larger number of blossoms than it could if it did not observe
this rule. This constancy in visiting the same kind of flower is
of great importance to plants, since it ensures that the pollen
will be conveyed to a flower of the same species as that from which
it came. But if all flowers were colored and perfumed alike, the
winged botanist could not identify the species; the pollen would be
constantly transferred to the stigmas of the wrong flowers, where it
would be useless, and so the work of cross-fertilization would be
seriously impeded.
A second cause contributing to the variety observed among flowers
is the desirability of attracting special kinds of insects. As
we have just seen, an insect does not visit all kinds of flowers
indiscriminately; neither, on the other hand, does a flower attract
indiscriminately all kinds of insects. Not only are injurious and
unprofitable visitors excluded, but the more specialized insects are
in greatest demand. Partiality for particular insects is shown both
by the shapes and coloring of flowers. Open shallow flowers, with
exposed honey accessible to almost all insects, have, as their most
frequent visitors, short-lipped flies and beetles. Many blossoms,
again, have become specially adapted to bees. Their honey is placed
beyond the reach of short-lipped fliers, and requires the slender
proboscis of a bee or butterfly for its extraction. Honeysuckle,
habenaria, plumbago, phlox, and narcissus illustrate a third type,
with flower-tubes so narrow and deep that their nectar is quite
inaccessible even to bees, and is reserved entirely for moths and
butterflies, which possess an extremely long and thin proboscis.
There is a corresponding adaptation in the colors; the gay tints of
the buttercup, poppy, and rose appear to have special attractions
for beetles; bees show a decided preference for blue, and this
color predominates in flowers whose shapes are adapted to their
visits. Deep tubular flowers specialized for Lepidoptera fall into
two divisions, according as they solicit the attentions of diurnal
butterflies or nocturnal moths. Red and purple are the favorite
colors of the former, while nocturnal moths show a preference for
white and pale flowers. Thus the carnation and campion (Lychnis
diurna), which open by day, have dark tints in comparison with
Lychnis respertina, which unfolds its petals toward evening. Almost
scentless by day, this white nocturnal flower diffuses a delicious
fragrance in the twilight. The evening primrose (Ænothera), which,
however, has yellow petals, is another example of this class. But
the most remarkable plant of this type is the night-flowering stock
(Cereus). Its pale blossoms open about seven in the evening, emit
puffs of odor from time to time, and close up again toward midnight;
by morning the flowers are withered. It is impossible to doubt
that we have in this instance a flower specialized for the visits
of nocturnal moths. The reason why nocturnal flowers, like the
honeysuckle and evening campion, have pale-colored petals is not
far to seek. These pale hues can be more easily distinguished at
night than the red or purple of Dianthus or Githago. Among lilies
both diurnal and nocturnal flowers occur, and clearly indicate by
their colors to which section of the Lepidoptera they are adapted.
The Turk’s-cap lily, with its perianth of fiery scarlet, is a
characteristic example of a diurnal flower adapted to butterflies
which wander abroad in daytime. On the other hand, Lilium Martagon,
an L. candidum, with their white bells, are nocturnal lilies
fertilized by night-loving moths.
Two flowers, unlike in their coloring, can hardly be equally
attractive to the same visitors, even if they grow together on the
same plant, as in the case of Arnebia; the presumption, therefore, is
that its spotted and pale blossoms are adapted for different insects.
Moreover, the stronger colors of the younger flowers correspond with
those of the day-blooming class, while the paler tints of those in
the second stage will render them more attractive to nocturnal moths;
and this view is strongly confirmed by the fact that night-blooming
flowers are never variegated, but have their petals uniformly devoid
of markings. By night the dark spots tend, in this instance, to
conceal the blossoms so much that, if these are to be converted into
nocturnal flowers, the removal of the spots is absolutely necessary.
We may therefore conclude with tolerable certainty that the flowers
of Arnebia in their first stage are adapted to bees and diurnal
Lepidoptera, while in their second condition they array themselves in
paler hues to attract nocturnal moths.
By the color change, in this instance, a diurnal is converted into
a nocturnal flower, and one advantage thereby gained is that the
blossoms appeal to a larger class of fertilizing agents. The more
restricted the circle of visitors on which any plant depends the
greater the risk, in the event of insects being scarce, of its
flowers remaining unfertilized and perishing. Here it would seem that
Nature proceeds on the same principle as a fisherman in changing
his bait. Like some other variable blossoms, Arnebia is in the
advantageous position of carrying two strings to her bow.
QUEER FLOWERS
--GRANT ALLEN
If Baron Munchausen had ever in the course of his travels come across
a single flower one standard British yard in diameter, fifteen
pounds avoirdupois in weight, and forming a cup big enough to hold
six quarts of water in its central hollow, it is not improbable that
the learned baron’s veracious account of the new plant might have
been met with the same polite incredulity which his other adventures
shared with those of Bruce, Stanley, Mendez Pinto, and Du Chaillu.
Nevertheless, a big blossom of this enormous size has been well known
to botanists ever since the beginning of the Nineteenth Century. When
Sir Stamford Raffles was taking care of Sumatra during our temporary
annexation, he happened one day to light upon a gigantic parasite,
which grew on the stem of a prostrate creeper in the densest part
of the tropical jungle. It measured nine feet round and three feet
across: it had five large petals with a central basin; and it was
mottled red in hue, being, in fact, in color and texture surprisingly
suggestive of raw beefsteak. One flower was open when Sir Stamford
came upon it: the other was in the bud, and looked in that state
extremely like a very big red cabbage. Specimens of this surprising
find were at once forwarded to England, and it was at last duly
labeled after the names of its two discoverers as Rafflesia Arnoldi.