CABBAGE-EATERS
One day Jacques came in from the garden with a cabbage root all covered
with warts having the shape and size of a pea. In each wart was a
little worm.
“Some of the cabbages are withering away,” announced the old gardener,
“though there are no worms on the leaves. I think the trouble comes
from the warts on the roots.”
“You have guessed right, my good Jacques,” replied Uncle Paul. “Leave
me that root and pull up all the cabbages that appear to you to be
affected. Of course you will burn all the diseased roots. By so doing
you will arrest the evil in the beginning, as the insect causing the
mischief is rare with us. The important thing is not to let it multiply
in the garden, even if we have to throw away many of the cabbages in
exterminating it.”
Uncle Paul’s instructions were followed, and no more warty roots have
been seen since. Next day the cabbage’s enemies were the subject of
conversation.
“Cultivated plants,” said Uncle Paul, “are more exposed to the ravages
of insects than the same plants in a wild state, because they are of a
finer flavor, tenderer, and of more luxuriant growth. Let us first
consider the cabbage, now that Jacques has furnished us the occasion.
“Look at this root, quite covered with ugly warts, hollow inside. I
open one. What do we find within? A small worm, a larva that would, if
left undisturbed, develop into a weevil with a beak that lies down on
the breast between the forelegs when the insect curls up and plays
dead. This weevil is known to men of science as belonging to a genus
called ceuthorhynchus, a name formed from two Greek words and meaning
snout-hider. It is black, with grayish hairs on the back and white
scales on the belly. Its thorax has a deep furrow and its wing sheaths
are ornamented with fine parallel grooves.
“It lays its eggs about the beginning of summer. The insect works its
way down to the root and punctures it here and there with its beak,
laying an egg in each puncture. In flowing around the wounded part the
sap of the plant forms a knob or fleshy wart in which the larva grows
until the end of October, when the worm leaves this nest to bury itself
in the ground, safe from the cold, and undergo transformation. The
punctured root exhausts its energies in bleeding sap to form the warts
occupied by the larvæ, so that the cabbage rapidly withers away; and in
this manner the cabbage-weevil makes itself an enemy much to be feared,
especially in England where it is extremely common. Nor does it confine
its depredations to cabbages; it attacks turnips also, and radishes and
rape.”
“This weevil seems to eat a good many things,” said Jules. “I thought
each kind of insect always fed on one particular plant.”
“You were not far wrong, my boy. In most cases insects have very
exclusive tastes, each confining itself to one kind of plant and
disdaining all others. Sometimes, however, they vary their diet, and as
they are connoisseurs, very well up on vegetable flavors, in changing
their food they choose plants having nearly identical nutritive
properties, taste, and smell. Do not we ourselves find in the radish
and the turnip something of the smell and taste of the cabbage?”
“That’s so,” assented Louis.
“We find more or less similarity in the qualities characteristic of a
great many other plants grouped together by botanists in the family of
cruciferæ and including, for instance, the cress, the radish, and
colza.”
“Botanists, cruciferæ—I don’t know very well what those are,” said
Emile.
“No, those are strange words to you. Botanists are learned persons who
spend their time studying plants and who tell us their names and
properties, differences and resemblances, where they grow and when they
blossom, with other matters of that sort.”
“And cruciferæ?”
“That word means cross-bearers and is applied to a large group of
plants with blossoms having four pieces or petals placed two by two,
opposite each other, so as to form a sort of cross. A good example is
the colza blossom. Plants with cross-shaped flowers include the
cabbage, rape, turnip, radish, clove, colza, cress, and many others.”
“They are all cruciferæ?”
“Yes, all cruciferæ. But their likeness is not confined to the shape of
the blossom; their inner properties also, such as smell, taste, and the
rest, are the same, or very nearly so. Consequently, the
cabbage-weevil, as knowing a little creature as can be found, goes to
the turnip when there are no cabbages to be had, to the colza if
turnips also are lacking, or to other plants still, but always to some
member of the cruciferæ family. Other insects show this same
peculiarity, each species having its particular group of plants and
going from one to another without ever making a mistake as to family.”
“Then they are expert botanists, I should say,” Jules remarked.
“One might almost think so; at least they show in their choice so keen
a discernment that often men of science go to school to them to learn
the various degrees of relationship in the plant world.”
“Oh, Uncle Paul, you are joking!” exclaimed Jules.
“Joking? Listen. You know the nasturtium, that beautiful orange-colored
flower ending at the bottom in a kind of horn; and you know the
mignonette, that sweet-smelling plant that Mother Ambroisine grows in
the window.”
“Yes, I know them.”
“Then tell me whether you find between mignonette, nasturtium, and
cabbage any resemblance, any sign of plant-relationship.”
“No, indeed! Those three plants are wholly unlike one another: their
flowers haven’t the same shape, nor their leaves, nor yet their fruit.”
“Well, my dear boy, you, who rather pride yourself on knowing something
about flowers, really know much less about them than a poor little
green caterpillar very common in our gardens; and many persons of far
more learning than you could take lessons from this same caterpillar.
It feeds indifferently on various cruciferæ, such as the cabbage, rape,
and the turnip; but it also feeds on the nasturtium and the mignonette.
Why? You must ask the scientists who make a thorough study of plants
and are determined to find out the minutest details concerning them.
They would tell you that there is something in their innermost
structure, something invisible to our untrained eyes, that makes the
nasturtium and the mignonette very nearly akin to the cruciferæ without
looking like them. It is enough to puzzle anybody, I admit. A worthless
caterpillar has, from the beginning of the world, eaten mignonette as
well as turnip, cabbage as well as nasturtium, and has been familiar
with plant-relationships unsuspected by science until our own time.”
“I should like to see this caterpillar that knows so much about
plants.”
“Your desire shall be gratified without delay.”