“These,” said Uncle George, “are what we grow our snowdrops and crocuses
from.”
As he spoke he handed each of the boys a few hard, round objects. Some
of these were small, white, and almost pear-shaped. The others were
larger, rounder, and brown in colour.
“The small white ones are snowdrop _bulbs_,” he continued. “The others
are crocus _corms_. There is a great difference between a bulb and a
corm, as we shall see when we examine and compare them.”
“The corm is covered with brown, papery skins, and has white buds on the
top of it,” said Frank.
“These brown skins are leaves,” remarked Uncle George.
“Leaves?” said Tom. “I thought all leaves were green.”
“Oh no, Tom, there are other leaves besides green leaves, called
scale-leaves. Green leaves, as you know, give off the moisture which the
roots take up from the soil. They also take in plant-food from the air.
Scale-leaves protect buds, flowers, and tender stems from cold and from
insects. These thin brown leaves of the crocus corm are scale-leaves
formed underground. Please remove the brown scale-leaves from one of the
corms, Frank.”
[Illustration]
1. Snowdrop.
2. Tulip.
3. Narcissus.
4. Crocus.
When Frank had done so, it was seen that these leaves were attached in
layers all round the corm. The corm was now a white, rounded lump. The
removal of the scale-leaves had left thin rings of leaf-marks; and on
these leaf-marks, here and there a tiny bud was seen.
“Now,” said Uncle George, “we can see that a corm is a stout, swollen,
underground stem. If you could imagine a horse-chestnut stem to be
squeezed up into a lump, you would have something like a corm. These
rings of leaf-marks are the nodes, where leaves and buds are found on
all stems. The large buds on the top of the corm correspond to the large
buds at the end of your horse-chestnut stem. Now, let us take off one of
these large top buds. Notice that it is covered with many tough,
protective scale-leaves.”
[Illustration: Crocus Bud Dissected.]
1. Scales.
2, 3, 4. Parts of Flower.
5. Leaves.
6. Spathe.
7. Ovary.
8. Young Corm. A. Old Corm.
Removing these scales, Uncle George came to a round object in the
centre.
“This,” he said, “is a long sack or bag. It contains the flower of the
crocus.”
Taking a needle, he carefully opened this up.
“Now, boys,” he said, “take your magnifiers and look carefully.”
Frank and Tom looked, and saw a curious little flower, surrounded by
four or five yellow needle-shaped things which, their uncle told them,
were the young green leaves of the crocus.
“Let us now,” he said, “examine the snowdrop bulb.
“Here we have thick, fleshy scale-leaves. If we remove them one by one,
we find that they are all attached to a flat, button-shaped stem.
Between the thick scale-leaves we see, here and there, a small side bud,
and on the top the baby snowdrop flower snugly wrapped up in their sack.
This protective sack is called a _spathe_.”
Uncle George then took from his pocket a very large bulb.
“This,” he said, “is the bulb of the narcissus or ‘white lily.’ It is
almost exactly like the snowdrop bulb, but it is larger, so that we can
see things much more distinctly.”
He then split the large bulb down the centre with his knife. With a pin
he pointed out the baby flower wrapped up in its spathe. All the parts
of the flower were seen, even the little seed-vessel containing the tiny
eggs, which become seeds after the flower has grown up.
“If you remember,” said Uncle George, “in our lesson on seeds we learned
that a seed contained a baby plant and a large supply of plant-food. I
am now going to show you that both the corm and the bulb contain a large
food supply. We have seen that the protective bud-scales in the corm are
tough and thin, while the stem is swollen and hard. In the bulb, on the
other hand, the bud-scales are thick and fleshy, while the stem is flat
and very small. If we place some of our crocus corms or snowdrop bulbs
in pure water, they will grow and flower just as well as if we had
planted them in the garden. What does this show us?”
“That, like the seeds which we grew in water, bulbs and corms contain a
store of food,” said Frank.
[Illustration]
A. Narcissus Bulb split open.
s., stem;
b., side buds;
s.l., scale-leaves;
f.l., leaves.
B. Snowdrop Bulb.
C. Flower of same Dissected out.
“That is correct, Frank. Let us put a corm and a bulb in water. Let us
also plant one of each in a pot of soil. We will watch them growing and
compare them from week to week.
“Now I am going to show you a simple experiment. You know that the food
we eat is drawn largely from plants. This food which we take from the
plant world is chiefly what the chemist calls _starch_. We have it in
bread, potatoes, rice, cornflour, and in nearly all the vegetables we
eat.
“I have here in this bottle a substance, called _iodine_, dissolved in
water. Anything containing _starch_ turns blue when touched with iodine.
Now observe what happens here.”
Uncle George poured some of the iodine into a saucer. He then dipped
into the iodine a piece of crocus corm, a thick scale of the snowdrop
bulb, soaked seeds of maize and wheat, a slice of raw potato, and a
piece of bread. Each at once turned dark blue on being dipped into the
liquid.
“Now, boys,” he said, “what do you learn from this?”
“The food store in bulbs and corms is the same as that in seeds,” said
Tom.
“The food supply of the bulb is contained in the thick, fleshy
scale-leaves, while in the corm it is in the stem,” said Frank.
“Very good,” said Uncle George. “It also shows us, I think, that we
ourselves owe a great deal to the plant world.”
Exercises on Lesson II.
1. Split an onion (or tulip bulb) down the centre, and compare it with
the snowdrop bulb. Draw it, giving special attention to the
middle part.
2. Take a potato and a crocus corm. Observe them both carefully, and
find out (1) how they resemble each other, and (2) how they
differ.
3. Explain how it is that a hyacinth grows so well in water.
4. Take any underground stem (_e.g._, iris or Solomon’s seal) and
compare it with a crocus corm. Notice the marks of underground
scale-leaves on the former.