SEEDS
CONDITIONS NECESSARY FOR SEEDS TO SPROUT
In the spring comes the great seed-planting time on the farm, in the
home garden and in the school garden. Many times the questions will be
asked: Why didn't those seeds come up? How shall I plant seeds so as
to help them sprout easily and grow into strong plants? To answer
these questions, perform a few experiments with seeds, and thus find
out what conditions are necessary for seeds to sprout, or germinate.
For these experiments you will need a few teacups, glass tumblers or
tin cans, such as tomato cans or baking-powder cans; a few plates,
either of tin or crockery; some wide-mouth bottles that will hold
about half a pint, such as pickle, olive, or yeast bottles or
druggists' wide-mouth prescription bottles; and a few pieces of cloth.
Also seeds of corn, garden peas and beans.
=Experiment.=--Put seeds of corn, garden peas, and beans (about a
handful of each) to soak in bottles or tumblers of water. Next day,
two hours earlier in the day, put a duplicate lot of seeds to soak.
When this second lot of seeds has soaked two hours, you will have two
lots of soaked seeds of each kind, one of which has soaked twenty-four
hours and the other two hours. Now take these seeds from the water and
dry the surplus water from them by gently patting or rubbing a few at
a time in the folds of a piece of cloth, taking care not to break the
skin or outer coating of the seed. Place them in dry bottles, putting
in enough to cover the bottoms of the bottles about three seeds deep;
cork the bottles. If you cannot find corks, tie paper over the mouths
of the bottles. Label the bottles "Seeds soaked 24 hours," "Seeds
soaked 2 hours," and let them stand in a warm place several days. If
there is danger of freezing at night, the bottles of seeds may be kept
in the kitchen or living room where it is warm, until they sprout.
Observe the seeds from day to day. The seeds that soaked twenty-four
hours will sprout readily (Fig. 36), while most, if not all, of those
that soaked only two hours will not sprout. Why is this? It is because
the two-hour soaked seeds do not receive sufficient moisture to carry
on the process of sprouting.
Our experiment teaches us that seeds will not sprout until they
receive enough moisture to soak them through and through.
This also teaches that when we plant seeds we must so prepare the soil
for them and so plant them that they will be able to get sufficient
moisture to sprout.
=Experiment.=--Soak some beans, peas or corn, twenty-four hours;
carefully dry them with a cloth. In one half-pint bottle place enough
of them to cover the bottom of the bottle two or three seeds deep;
mark this bottle A. Fill another bottle two-thirds full of them and
mark the bottle B (Fig. 37). Cork the bottles and let them stand for
several days. Also let some seeds remain soaking in the water. The few
seeds in bottle A will sprout, while, the larger number in bottle B
will not sprout, or will produce only very short sprouts. Why do not
the seeds sprout easily in the bottle which is more than half full?
To answer this question try the following experiment:
=Experiment.=--Carefully loosen the cork in bottle B (the bottle
containing poorly sprouted seeds), light a match, remove the cork from
the bottle and introduce the lighted match. The match will stop
burning as soon as it is held in the bottle, because there is no fresh
air in the bottle to keep the match burning. Test bottle A in the same
way. What has become of the fresh air that was in the bottles when the
seeds were put in them? The seeds have taken something from it and
have left bad air in its place; they need fresh air to help them
sprout, but they have not sprouted so well in bottle B because there
was not fresh air enough for so many seeds. The seeds in the water do
not sprout because there is not enough air in the water. Now try
another experiment.
[Illustration: FIG. 36.
To show that seeds need water for germination. The beans in bottle _A_
were soaked 2 hours, those in bottle _B_ were soaked 24 hours. They
were then removed from the water and put into dry bottles.]
[Illustration: FIG. 37.
To show that seeds need air for germination. The beans in both bottles
were soaked 24 hours, and then were put into dry bottles Bottle _A_
contained sufficient air to start the few seeds. Bottle _B_ had not
enough. The water in the tumbler _C_ did not contain sufficient air
for germination. See experiment, page 72.]
[Illustration: FIG. 38.
To show that seeds need air for germination. Corn planted in puddled
clay in tumbler _A_ could not get sufficent air for sprouting. The
moist sand in tumbler _B_ admitted sufficient air for germination.]
=Experiment.=--Fill some tumblers or teacups or tin cans with wet sand
and others with clay that has been wet and then thoroughly stirred
till it is about the consistency of cake batter or fresh mixed mortar.
Take a tumbler of the wet sand and one of the wet clay and plant two
or three kernels of corn in each, pressing the kernels down one-half
or three-quarters of an inch below the surface; cover the seeds and
carefully smooth the surface. In other tumblers plant peas, beans, and
other seeds. Cover the tumblers with saucers, or pieces of glass or
board to keep the soil from drying. Watch them for several days. If
the clay tends to dry and crack, moisten it, fill the cracks and
smooth the surface. The seeds in the sand will sprout but those in the
clay will not (see Fig. 38). Why is this? Water fills the small spaces
between the particles of clay and shuts out the fresh air which is
necessary for the sprouting of the seeds.
This teaches us that when we plant seeds we must so prepare the soil,
and so plant the seeds that they will get enough fresh air to enable
them to sprout, or, in other words, the soil must be well ventilated.
=Experiment.=--Plant seeds of corn and beans in each of two tumblers;
set one out of doors in a cold place and keep the other in a warm
place in the house. The seeds kept in the house will sprout quickly
but those outside in the cold will not sprout at all. This shows us
that seeds will not sprout without heat.
If the weather is warm place one of the tumblers in a refrigerator.
Why don't we plant corn in December?
Why not plant melons in January?
Why not plant cotton in November?
The seeds of farm crops may be divided into two classes according to
the temperatures at which they will germinate or sprout readily and
can be safely planted.
Class A. Those seeds that will germinate or sprout at an average
temperature of forty-five degrees in the shade, or at about the time
the peach and plum trees blossom:
Barley Beet Parsley
Oats Carrot Parsnip
Rye Cabbage Onion
Wheat Cauliflower Pea
Red Clover Endive Radish
Crimson Clover Kale Turnip
Grasses Lettuce Spinach
These can be planted with safety in the spring as soon as the ground
can be prepared, and some of them, if planted in the fall, live
through the winter.
Class B. Those seeds that will germinate or sprout at an average
temperature of sixty degrees in the shade, or when the apple trees
blossom:
Alfalfa Soy Bean Squash
Cow Pea Pole Bean Cucumber
Corn String Bean Pumpkin
Cotton Melon Tomato
Egg Plant Okra Pepper
We are now ready to answer the question: What conditions are necessary
for seeds to sprout or germinate? These conditions are:
The presence of enough moisture to keep the seed thoroughly soaked.
The presence of fresh air.
The presence of more or less heat.
This teaches us that when we plant seeds in the window box or in the
garden or on the farm we must so prepare the soil and so plant the
seeds that they will be able to obtain sufficient moisture, heat, and
air for sprouting. The moisture must be film water, for if it is free
water or capillary water filling the soil pores, there can be no
ventilation and, therefore, no sprouting.
SEED TESTING
In a previous experiment (page 73) the seeds planted in the wet clay
did not sprout (see Fig. 38). In answer to the question, "Why is
this?" some will say the seeds were bad. It often happens on the farm
that the seeds do not sprout well and the farmer accuses the seedsman
of selling him poor seed, but does not think that he himself may be
the cause of the failure by not putting the seeds under the proper
conditions for sprouting. How can we tell whether or not our seeds
will sprout if properly planted? We can test them by putting a number
of seeds from each package under proper conditions of moisture, heat
and air, as follows:
For large seeds take two plates (see Fig. 39) and a piece of cloth as
wide as the bottom of the plate and twice as long. Count out fifty or
one hundred seeds from a package, wet the cloth and wring it out.
Place one end of the cloth on the plate, place the seeds on the cloth
and fold the other end of the cloth over them. On a slip of paper mark
the number of seeds and date, and place on the edge of the plate. Now
cover the whole with another plate, or with a pane of glass to keep
from drying. Set the plate of seeds in a warm room and examine
occasionally for several days. If the cloth tends to dry, moisten it
from time to time. As the seeds sprout take them out and keep a record
of them. Or leave them in the plate and after four or five days count
those that have sprouted. This will give the proportion of good seeds
in the packages.
For small seeds fold the cloth first and place the seeds on top of it.
Another good tester for small seeds is made by running about an inch
of freshly mixed plaster of Paris into a small dish or pan and
moulding flat cavities in the surface by setting bottles into it. The
dish or pan and bottles should be slightly greased to prevent the
plaster sticking to them. When the cast has hardened it should be
turned out of the mould and set in a large dish or pan. One hundred
small seeds are then counted out and put into one of the cavities,
others are put into the other cavities. Water is then poured into the
pan till it rises half way up the side of the plaster cast or porous
saucer. The whole thing is then covered to keep in the moisture (Fig.
40).
Another method is to get boxes of finely pulverized sand or soil and
carefully plant in it fifty or one hundred seeds of each kind to be
tested. Then by counting those that come up, the proportion of good
seeds can easily be found.
In every case the testers should be kept at a temperature of about
seventy degrees or about that of the living room.
HOW THE SEEDS COME UP
Plant a few seeds of corn, beans and garden peas in boxes or tumblers
each day for several days in succession. Then put seeds of corn, beans
and garden peas to soak. After these have soaked a few hours, examine
them to find out how the seed is constructed. Note first the general
shape of the seeds and the scar (Fig. 41-4) on one side as in the bean
or pea and at one end or on one edge in the corn. This scar, also
called hilum, is where the seed was attached to the seed vessel.
Cut into the bean and pea, they will be found to be protected by a
tough skin or coat. Within this the contents of the seed are divided
into two bodies of equal size lying close to each other and called
seed leaves or cotyledons (Fig. 41-5). Between them near one end or
one side will be found a pair of very small white leaves and a little
round pointed projection. The part bearing the tiny leaves was
formerly, and is sometimes now, called the plumule, but is generally
called the epicotyl, because it grows above or upon the cotyledons.
The round pointed projection was formerly called the radicle, but is
now spoken of as the hypocotyl, because it grows below or under the
cotyledons.
Examine a dry kernel of corn and notice that on one side there is a
slight oval-shaped depression (Fig. 41-1). Now take a soaked kernel
and cut it in two pieces making the cut lengthwise from the top of the
kernel through the centre of the oval depression and examine the cut
surface. A more or less triangular-shaped body will be found on the
concave side of the kernel (see Figs. 41-2 and 41-3). This is the one
cotyledon of the corn. Besides this will be found quite a mass of
starchy material packed in the coverings of the kernel and in close
contact with one side of the cotyledon. This is sometimes called the
endosperm.
Within the cotyledon will be found a little growing shoot pointed
toward the top of the kernel. This is the epicotyl, and another
growing tip pointed toward the lower end of the kernel; this is the
hypocotyl or the part which penetrates the soil and forms roots.
Now examine the seeds that were planted in succession. Some will be
just starting a growing point down into the soil. Some of them have
probably come up and others are at intermediate stages.
How did the bean get up?
After sending down a root the hypocotyl began to develop into a strong
stem which crooked itself until it reached the surface of the soil and
then pulled the cotyledons or seed-leaves after it (Fig. 42). These
turn green and after a time shrink and fall off.
The pea cotyledons were left down in the soil, the epicotyl alone
pushing up to the surface. The corn pushed a slender growing point to
the surface leaving the cotyledon and endosperm behind in the soil but
still attached to the little plant (Fig. 43).
USE OF COTYLEDONS AND ENDOSPERM
=Experiment.=--Plant some beans in a pot or box of soil and as soon as
they come up cut the seed-leaves from some of them and watch their
growth for several days. It will soon be seen that the plants on which
the seed-leaves were left increase in size much more rapidly than
those from which the seed-leaves were removed (see Figs. 43 and 44).
Sprout some corn in the seed tester. When the seedlings are two or
three inches long, get a wide-mouthed bottle or a tumbler of water and
a piece of pasteboard large enough to cover the top. Cut a slit about
an eighth of an inch wide from the margin to the centre of the
pasteboard disk. Take one of the seedlings, insert it in the slit,
with the kernel under the pasteboard so that it just touches the
water. Take another seedling of the same size, carefully remove the
kernel from it without injuring the root, and place this seedling in
the slit beside the first one (Fig. 45). Watch the growth of these two
seedlings for a few days. Repeat this with sprouted peas. In each case
it will be found that the removal of the seed-leaves or the kernel
checks the growth of the seedling. Therefore, it must be that the
seed-leaves which appear above ground, as in the case of the bean, or
the kernel of the corn which remains below the surface of the soil,
furnish the little plant with food until its roots have grown strong
enough to take sufficient food from the soil.
[Illustration: FIG. 39.
A seed-tester, consisting of two plates and a moist cloth.]
[Illustration: FIG. 40.--A SEED-TESTER.
A plaster cast with cavities in the surface for small seeds.]
[Illustration: FIG. 41.
1. Corn-kernel showing depression at _z_. 2. Section of same after
soaking. 3. Corn-kernel after germination has begun. The seed-coat _a_
has been partly removed. 4. Bean showing scar or hilum at _h_. 5. The
same, split open. 6. Bean with one cotyledon removed, after sprouting
had begun. _a_, Seed-coat; _b_, cotyledon; _c_, epicotyl; _d_,
hypocotyl; _e_, endosperm. (Drawings by M.E. Feltham.)]