But it is not only necessary that the flowers should keep their
honey for the insects, they also have to take care and keep it
for the right kind of insect. Ants are in many cases great
enemies to them, for they like honey as much as bees and
butterflies do, yet you will easily see that they are so small
that if they creep into a flower they pass the anthers without
rubbing against them, and so take the honey without doing any
good to the plant. Therefore we find numberless contrivances for
keeping the ants and other creeping insects away. Look for
example at the hairy stalk of the primrose flower; those little
hairs are like a forest to a tiny ant, and they protect the
flower from his visits. The Spanish catchfly (Silene otites), on
the other hand, has a smooth, but very gummy stem, and on this
the insects stick, if they try to climb. Slugs and snails too
will often attack and bite flowers, unless they are kept away by
thorns and bristles, such as we find on the teazel and the
burdock. And so we are gradually learning that everything which
a plant does has its meaning, if we can only find it out, and
that even very insignificant hair has its own proper use, and
when we are once aware of this a flower-garden may become quite a
new world to us if we open our eyes to all that is going on in
it.
But as we cannot wander among many plants to-day, let us take a
few which the bees visit, and see how they contrive not to give
up their honey without getting help in return. We will start
with the blue wood-geranium, because from it we first began to
learn the use of insects to flowers.
More than a hundred years ago a young German botanist, Christian
Conrad Sprengel, noticed some soft hairs growing in the centre of
this flower, just round the stamens, and he was so sure that
every part of a plant is useful, that he set himself to find out
what these hairs meant. He soon discovered that they protected
some small honey-bags at the base of the stamens, and kept the
rain from washing the honey away, just as our eyebrows prevent
the perspiration on our faces from running into our eyes. This
led him to notice that plants take great care to keep their honey
for insects, and by degrees he proved that they did this in order
to tempt the insects to visit them and carry off their pollen.
The first thing to notice in this little geranium flower is that
the purple lines which ornament it all point directly to the
place where the honey lies at the bottom of the stamens, and
actually serve to lead the bee to the honey; and this is true of
the veins and marking of nearly all flowers except of those which
open by night, and in these they would be useless, for the
insects would not see them.
When the geranium first opens, all its ten stamens are lying flat
on the corolla or coloured crown, as in the left-hand flower in
Fig. 58, and then the bee cannot get at the honey. But in a
short time five stamens begin to raise themselves and cling round
the stigma or knob at the top of the seed-vessel, as in the
middle flower. Now you would think they would leave their dust
there. But no! the stigma is closed up so tight that the dust
cannot get on to the sticky part. Now, however, the bee can get
at the honey-glands on the outside of the raised stamens; and as
he sucks it, his back touches the anthers or dust-bags, and he
carries off the pollen. Then, as soon as all their dust is gone,
these five stamens fall down, and the other five spring up.
Still, however, the stigma remains closed, and the pollen of
these stamens, too, may be carried away to another flower. At
last these five also fall down, and then, and not till then, the
stigma opens and lays out its five sticky points, as you may see
in the right-hand flower, Fig. 58.
But its own pollen is all gone, how then will it get any? It
will get it from some bee who has just taken it from another and
younger flower; and thus you see the blossom is prevented from
using its own pollen, and made to use that of another blossom, so
that its seeds may grow healthy and strong.
The garden nasturtium, into whose blossom we saw the humble-bee
poling his head, takes still more care of its pollen-dust. It
hides its honey down at the end of its long spur, and only sends
out one stamen at a time instead of five like the geranium; and
then, when all the stamens have had their turn, the sticky knob
comes out last for pollen from another flower.
All this you may see for yourselves if you find geraniums* in the
hedges, and nasturtiums in you garden. But even if you have not
these, you may learn the history of another flower quite as
curious, and which you can find in any field or lane even near
London. The common dead-nettle (Fig. 59) takes a great deal of
trouble in order that the bee may carry off its pollen. When you
have found one of these plants, take a flower from the ring all
round the stalk and tear it gently open, so that you can see down
its throat. There, just at the very bottom, you will find a
thick fringe of hairs, and you will guess at once that these are
to protect a drop of honey below. Little insects which would
creep into the flower and rob it of its honey without touching
the anthers of the stamens cannot get past these hairs, and so
the drop is kept till the bee comes to fetch it. (*The scarlet
and other bright geraniums of our flower-gardens are not true
geraniums, but pelargoniums. You may, however, watch all these
peculiarities in them if you cannot procure the true wild
geranium.)
Now look for the stamens; there are four of them, two long and
two short, and they are quite hidden under the hood which forms
the top of the flower. How will the bee touch them? If you were
to watch one, you would find that when the bee alights on the
broad lip and thrusts her head down the tube, she first of all
knows her back against the little forked tip. This is the sticky
stigma, and she leaves there any dust she has brought from
another flower; then, as she must push far in to reach the honey,
before she comes out again has carried away the yellow powder on
her back, ready to give it to the next flower.
Do you remember how we noticed at the beginning of the lecture
that a bee always likes to visit the same kind of plant in one
journey? You see now that this is very useful to the flowers.
If the bee went from a dead-nettle to a geranium, the dust would
be lost, for it would be of no use to any other plant but a dead-
nettle. But since the bee likes to get the same kind of honey
each journey, she goes to the same kind of flowers, and places
the pollen-dust just where it is wanted.
There is another flower, called the Salvia, which belongs to the
same family as our dead-nettle, and I think you will agree with
me that its way of dusting the bee's back is most clever. The
Salvia (Fig. 60) is shaped just like the dead-nettle, with a hood
and a broad lip, but instead of four stamens it has only two, the
other two being shrivelled up. The two that are left have a very
strange shape, for the stalk or filament of the stamen is very
short, while the anther, which is in most flowers two little bags
stuck together, has here grown out into a long thread, with a
little dust-bag at one end only. In 1, Fig. 60, you only see
one of these stems, because the flower is cut in half, but in the
whole flower, one stands on each side just within the lip. Now,
when the bee puts her head into the tube to reach the honey, she
passes right between these two swinging anthers, and knocking
against the end pushes it before her and so brings the dust-bag
plump down on her back, scattering the dust there! you can
easily try this by thrusting a pencil into any Salvia flower, and
you will see the anther fall.
You will notice that all this time the be does not touch the
sticky stigma which hangs high above her, but after the anthers
are empty and shrivelled the stalk of the stigma grows longer,
and it falls lower down. By-and-by another bee, having pollen on
her back, comes to look for honey, and as she goes into No. 3,
she rubs against the stigma and leaves upon it the dust from
another flower.
Tell me, has not the Salvia, while remaining so much the same
shape as the dead-nettle, devised a wonderful contrivance to make
use of the visits of the bee?
The common sweet violet (Viola odorata) or the dog violet (Viola
canina), which you can gather in any meadow, give up their
pollen-dust in quite a different way from the Salvia, and yet it
is equally ingenious. Everyone has noticed what an irregular
shape this flower has, and that one of its purple petals has a
curious spur sticking out behind. In the tip of this spur and in
the spur of the stamen lying in it the violet hides its honey,
and to reach it the bee must press past the curious ring of
orange-tipped bodies in the middle of the flower. These bodies
are the anthers, Fig. 61, which fit tightly round the stigma, so
that when the pollen-dust, which is very dry, comes out of the
bags, it remains shut in by the tips as if in a box. Two of
these stamens have spurs which lie in the coloured spur of the
flower, and have honey at the end of them. Now, when the bee
shakes the end of the stigma, it parts the ring of anthers, and
the fine dust falls through upon the insect.
Let us see for a moment how wonderfully this flower is arranged
to bring about the carrying of the pollen, as Sprengel pointed
out years ago. In the first place, it hangs on a thin stalk, and
bends its head down so that the rain cannot come near the honey
in the spur, and also so that the pollen-dust falls forward into
the front of the little box made by the closed anthers. Then the
pollen is quite dry, instead of being sticky as in most plants.
This is in order that it may fall easily through the cracks.
Then the style or stalk of the stigma is very thin and its tip
very broad, so that it quivers easily when the bee touches it,
and so shakes the anthers apart, while the anthers themselves
fold over to make the box, and yet not so tightly but that the
dust can fall through when they are shaken. Lastly, if you look
at the veins of the flower, you will find that they all point
towards the spur where the honey is to be found, so that when the
sweet smell of the flower has brought the bee, she cannot fail to
go in at the right place.
Two more flowers still I want us to examine together, and then I
hope you will care to look at every flower you meet, to try and
see what insects visit it, and how its pollen-dust is carried.
These two flowers are the common Bird's-foot trefoil (Lotus
corniculatus), and the Early Orchis (Orchis mascula), which you
may find in almost any moist meadow in the spring and early
summer.
The Bird's-foot trefoil, Fig. 62, you will find almost anywhere
all through the summer, and you will know it from other flowers
very like it by its leaf, which is not a true trefoil, for behind
the three usual leaflets of the clover and the shamrock leaf, it
has two small leaflets near the stalk. The flower, you will
notice, is shaped very like the flower of a pea, and indeed it
belongs to the same family, called the Papilionaceae or butterfly
family, because the flowers look something like an insect flying.
In all these flowers the top petal stands up like a flag to catch
the eye of the insect, and for this reason botanists call it the
"standard". Below it are two side-petals called the "wings," and
if you pick these off you will find that the remaining two petals
are joined together at the tip in a shape like the keel of a
boat. For this reason they are called the "keel". Notice as we
pass that these two last petals have in them a curious little
hollow or depression, and if you look inside the "wings" you will
notice a little knob that fits into this hollow, and so locks the
two together. We shall see by-and-by that this is important.