By FREDERICK LEROY SARGENT.
In the various names which the dandelion has received, we see expressed,
for the most part, either a reference to the tooth-like recurved lobes of
the leaves, Fig. 1, or an allusion to the medicinal properties of the
plant. Thus, our English name is a modified form of the French _dent de
lion_, meaning lion's tooth, and in German we have the same idea expressed
in _Loewenzahn_. Fifty years ago this plant appeared in the botanies as
_Leontodon taraxicum_, the generic name being derived from the Greek
_leon_, lion, and _odons_, tooth, and the specific from the Greek
_tarasso_, to stir up, in reference to the effect of a dose. In later
works we find the genus _Leontodon_, including the "fall dandelion" (_L.
autumnale_), but not the true dandelion, which now appears in a genus by
itself under the name _Taraxicum Densleonis_. Here the specific name is
merely "lion's tooth" again, in Latin.
[Illustration: FIG. 1.]
Finally, in the latest works our plant is given as _Taraxicum officinale_,
since this has been found to be the name which, according to the rules of
botanical nomenclature, takes precedence of all others. An allusion to the
teeth is thus no longer retained, the only reference remaining being to
the plant's officinal use.
To the majority of people the mention of the dandelion calls to mind not
so much its medicinal properties as its use for food. Although its
cultivation, either as a spring pot herb or as a salad with blanched
leaves, is comparatively modern, the wild plant seems to have been long
valued as a vegetable. There is reason to believe that the Romans made use
of it as a pot herb, and Chinese writers of the fourteenth century mention
its being eaten in their country, although there is no evidence of
cultivation at that time.
There are but few of our flowering plants that grow so widespread over the
world. It occurs in North America from the Atlantic to the Pacific coast,
in Europe, in Asia, and in the Arctic regions. This extensive range may in
part be accounted for by the fact that our plant belongs to the large and
aggressive family of the _Compositae_, and is thus related to such invaders
as daisies, burdocks, and thistles. Still, the dandelion has more to
recommend it than mere family connection; for, despite its lowly aspect,
it is no poor relation, but, as we shall hope to show in the present
article, it has many virtues of its own which entitle it to respect.
Prominent among these is its adaptability to the different conditions
under which it grows. It seems to make the best of everything. If by
chance a seed falls upon poor, thin soil, the young plant sends forth, as
rapidly as possible, a rosette of leaves pressed close to the earth. And
thus, on the principle that "possession is nine points of the law," it
secures for its roots the use of a certain amount of territory quite safe
from the encroachments of other plants. In rich ground the case is quite
different, for here there is so much nutriment in a small quantity of
earth, that the struggle for soil is not such a life and death matter as
in the less favored localities. Consequently we find a large number of
plants crowded together as close as they can stand; and it is obvious that
if, under these circumstances, the dandelion should develop a flat rosette
of leaves, the grass and other plants growing around would soon overshadow
it, and it would have small chance for life.
Our plant, therefore, extends its leaves upward, and does its best to
elongate them so as to keep pace with the growth of its rivals. But as
these are for the most part grasses and plants which grow by elongation of
the stem, the race for sunshine is rather in favor of these other plants,
for the reason that a given amount of material put into a stem makes a
stiffer organ than when put into a leaf. Still, even with these odds
against it, the dandelion seems well able to hold its own, for it probably
derives more or less advantage from the recurved lobes, or teeth, which
give the plant its name. These are admirably fitted to act in much the
same manner as a ratchet; and when the neighboring grasses are blown
against the dandelion, a blade may slide along the margin of the leaf
toward the base; but, as it springs back from its own elasticity, it
cannot slide in the opposite direction, for a tooth will catch it, and
thus force it to help support the leaf, and hold it up to the sunshine. We
need not stop to consider how the dandelion behaves in soil which is
neither very rich nor very poor, for enough has been said to show that it
has not much to fear from any rivals it may meet under ordinary
circumstances.
It is not only against the aggressions of neighboring plants, however,
that our dandelion needs to be prepared. It is at least equally important
for its welfare that it have some means of protection against herbivorous
animals--not only such as might eat its leaves, but also the more stealthy
ones that live upon the food which plants store underground. All such foes
it thwarts by a means as simple as it is efficient. Every part of the
plant contains a milky juice which is intensely bitter, and a first taste
is quite enough to convince the most stupid animal that raw dandelion is
not good eating, and most animals know enough to let it severely alone.
Curiously enough, however, in this, as in many other cases, it happens
that what in nature acts to deter animals from eating the plant, with man
offers the chief attraction, for it is this very bitter principle
(_taraxacin_) which gives to dandelion greens their peculiar flavor, and
affords the essential element in the extract which physicians prescribe.
The store of food, referred to above, which the dandelion accumulates in
its root, not infrequently enables it to pass, almost unharmed, through
dangers that with less provident plants would surely prove fatal. For
example, it must often happen that from drought or from being trampled
upon by animals, the leaves become wholly or in part destroyed. Now, if
there were no reserve store of food, the plant would have no chance of
rallying; but as it is, this food supplies the material for new growth,
and upon the return of favorable conditions, fresh leaves are developed,
and the plant lives on as before. Primarily, of course, the purpose of
this storage of food is to enable the plant to live on from year to year,
resting in the winter, and in the spring beginning work again with a good
start.
In comparing the higher with the lower plants, the superiority of the
former is most beautifully shown in the better provision which is made for
the welfare of offspring; and in this regard our dandelion stands among
the highest. Before we can understand the ways in which our little plant
performs this part of its life work, we must briefly consider the
structure of the blossom.
[Illustration: FIG. 2.]
If with a sharp knife we cut a blossom in halves, from the stem upward,
the parts represented in Fig. 2 will be disclosed. Surmounting the stalk
is a cushion-like receptacle, R, from the top of which arise a number of
tiny flowers, F, while from the side grow out a series of green scales, S,
forming an involucre around the whole. A single one of these florets, Fig.
3, exhibits the following parts: First, a bright yellow corolla, C O,
tubular below, but strap-shaped above, as if a tube had been split for
part of the way on one side, and the upper part flattened. Second, five
stamens, S K, attached by slender filaments, F M, to the tubular part of
the corolla, and with their anthers or pollen sacs, A N, joined together
by the edges to form a tube. Third, a single pistil having a long style, S
Y, which, above, passes through the anther tube, and bears at its end two
diverging stigmas, S G, and below connects by a short neck, N, with the
small ovary, O, which contains a solitary ovule. Fourth, a calyx, C X,
composed of numerous slender bristles.
[Illustration: FIG. 3.]
The purpose of these complex structures is, of course, in one way or
another to secure the development of the ovule into a seed fitted to
produce a new plant. This development will proceed only after the ovule
has been influenced (_i. e._, fertilized) by pollen placed upon the
stigma; but when once the mysterious process of fertilization has taken
place, then there follows immediately those wonderful changes in the
blossom which culminate in the ripening of the fruit.
There are but two possible ways in which fertilization may be secured;
either the pollen which affects the ovule must come from the same flower
(then called close fertilization), or the pollen must come from another
flower of the same kind (cross fertilization). Now, while either of these
methods will insure the production of a seed, numerous experiments go to
show that those offspring which result from cross fertilization are in
many ways superior to those which are produced from close fertilization;
and it is to the advantages of cross fertilization that we have to look
for an explanation of the significance of many peculiar structures, not
only of the dandelion, but of flowers in general.
It is obvious that, to secure cross fertilization, there must be some
agent to transfer the pollen from one plant to another. Most commonly,
either the wind is taken advantage of for this purpose, as with elms,
pines, grasses, etc., or else flying insects are induced to perform the
office, as is the case with the majority of our familiar flowers. The wind
is a very wasteful carrier, so that for every grain that is properly
placed, thousands, or even millions, may be lost. Insects, on the
contrary, waste but little; and, moreover, as Aristotle so shrewdly
observed, they habitually confine their visits, for a number of trips,
exclusively to the flowers of one species.
The dandelion seems to fully appreciate the great advantages of securing
the services of insects, for it appeals most strongly to their love of
bright colors and their passion for sweets. As the flowers open, each tiny
golden cup is filled to the brim with purest nectar, and he must be a very
dull insect, indeed, that cannot see the brilliant head of flowers as far
as he can see anything. At any rate, it is not the dandelion's fault if he
does not, for the blossom is placed where it will be as conspicuous as
possible. If the surrounding herbage is tall, the flower stalk is
elongated, so that the crown of flowers may not be obscured. If the plants
around are low-lying, it would be wasteful to have a long stalk, so it has
a short one, sometimes so short that the blossom looks like a button in
the center of the leaf rosette. Economy of material is furthermore shown
in the fact that the stalk is always hollow, for it is a principle well
known to builders that, when there is required a pillar of a given
strength, less material is needed for the tubular form than for the solid
cylinder.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
But to return to our flower. We have next to consider how the visits of
insects are utilized to secure cross fertilization. If we examine the
anther tube of a flower that has just opened, Fig. 4, we shall see that
the style has not yet protruded, but fills the entire cavity, except such
space as is occupied by a quantity of pollen which the anthers have shed.
So much of the style as is within the tube is thickly beset with hairs
that point upward; and when the lower portion elongates, this hairy part
brushes the pollen out of the tube, and protrudes, covered with the yellow
dust, Fig. 5. At this stage, an insect coming for nectar must rub against
the style, and so become more or less covered with pollen. None of it,
however, can get upon the stigmas, for they are not yet exposed. After a
short time has elapsed, during which much of the pollen has probably been
rubbed off, the style is seen to split at the top; and as the halves
separate and roll back, Fig. 3, their inner faces (the stigmas) are
exposed. If, now, the flower be visited by an insect which has previously
been to a younger flower, the pollen he brings will be deposited upon the
stigmas as he rubs against them, and cross fertilization will be effected.
Let us suppose, however, that no insect visits the blossom--and this must
often happen to such as appear very early in the spring or late in the
fall, when hardly any insects are around. In such cases we find that seeds
are produced, and therefore we must infer that fertilization has in some
way or other been secured. An examination of a flower still older than any
we have considered, Fig. 6, will show us what takes place. Here it will be
seen that, after the stigmas have diverged, they continue to roll back,
until a coil of one or more turns has been made; and as a result of this
the stigmatic surface comes in contact with the hairs on the style, and
touches the pollen grains entangled by them. Still, the close
fertilization thus accomplished is only a last resort, and it can only
occur in the event of insects' visits having failed; for when pollen from
another flower has once fallen on the stigma, no pollen coming afterward
can have the least effect. Thus, we have another instance of the
dandelion's ability to make the best of its surroundings.
[Illustration: FIG. 6.]
It even adapts itself to the weather; for when the sun shines, the scales
of the involucre bend back, and the blossom is expanded to its fullest
extent; but in dull weather, or at night, the scales bend inward, and the
blossom is tightly closed. The advantages of this remarkable movement,
with its implied sensitiveness, is obvious when we consider that insects
are abroad only in sunshine, while at other times there is danger of dew
or rain getting into the nectar, and so spoiling it for the insects.
After fertilization has been accomplished throughout the blossom, the
involucre closes, and remains closed during the ripening of the fruit. The
changes which now take place are as follows: In each flower the corolla,
stamens, and style, being of no further use, wither, and sever their
connection with the ovary; the ovule develops into a seed containing a
tiny plantlet well provided with food for its use during germination; the
ovary grows to keep pace with the seed, its tissues become hardened, and a
number of spine-like projections develop near the upper part; and finally
the short neck which bears the calyx bristles elongates, pushing upward
the withered parts of the flower. At this stage the involucral scales bend
back through an arc of about 180 deg., the cushion-like receptacle becomes
almost spherically convex, the fruits radiate in all directions, the
bristles spread, and a beautiful cluster of little parachutes is presented
to the wind.
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
Even a glance at one of these fruits, Fig. 7, is sufficient to discover a
wonderful fitness for transportation by wind, and more careful study shows
that this fitness pervades every detail. For example, on examining the
bristles microscopically, Fig. 8, it is shown that they are not simple
threads, but each is hollow and has numerous projections extending on
either side, all of which serves to increase the buoyancy in a very
effective way.
The experience of aeronauts has shown that a highly important part in the
equipment of a balloon, after the attainment of buoyancy, is the provision
of some means of arresting the balloon's progress when the destination has
been reached. One of the most successful means which they employ is the
grappling hook; and as we find the base of our diminutive parachute
provided with a number of upwardly directed spines, it seems fair to
conclude that these serve to arrest the fruit upon favorable soil. If it
comes to rest upon a smooth surface--which, of course, would be
barren--the next breeze would easily blow it away; but if it chance to
fall on soil or among other plants, the effect of the spines would be to
retain it against the power of even a strong wind. Thus, we may leave it
safely landed upon good soil, ready to begin under favorable conditions
the cycle of its wonderful life.--_Popular Science News._