GERMINATION
“The germ in the heart of the seed is in a state that may be likened to
deep sleep: its life is, as it were, arrested, suspended. But under the
stimulus of certain conditions it awakens, throws off its coverings,
gathers strength from its stored-up food, unfolds its first leaves, and
appears above ground. This opening of the seed is called germination.
Moisture, warmth, and air are the determining causes; without their
coöperation the seed would remain a certain length of time in good
condition for sowing, after which it would wither and lose its
germinating power.
“No seed germinates without the help of moisture. Water plays a
multiple part. First it soaks into the germ and the parts surrounding
it, causing these to swell more than the envelope, so that the latter,
however hard a shell it may be, is burst open. Through the cracks of
this broken envelope the gemmule pushes out on one side and the radicle
on the other, and henceforth the little plant enjoys the benefit of sun
and air. Germination is more or less slow according to the degree of
resistance offered by the walls of the seed. If these are hard and
stony it is only with extreme slowness that the germ absorbs moisture
and manages to burst its cell. Therefore, to shorten the period of
germination care is taken to thin the shells of excessively hard seeds
by rubbing them with a stone.
“Besides the mechanical part played by water in opening the seed, it
has still another relating to nutrition. The various changes undergone
by the alimentary contents of the perisperm and the cotyledons in
becoming liquefied and capable of absorption cannot take place without
the aid of water. Furthermore, this liquid is indispensable for
dissolving the nutritive ingredients, introducing them into the young
plant, and distributing them evenly throughout. It is plain, then, that
if the seed remains dry it is absolutely impossible for it to
germinate, and that in order to preserve seeds the first condition is
to protect them from moisture.
“With moisture there must also be warmth. As a general rule,
germination proceeds most satisfactorily when the thermometer registers
between ten and twenty degrees centigrade, our spring and autumn
temperature. Outside these limits, be it above or below, germination is
retarded, ceasing altogether in extreme temperatures.
“The coöperation of air is not less necessary. Seeds might have the
proper temperature and sufficient moisture, but if air were lacking
germination would not follow. This capital condition explains to us why
seeds planted too deep fail to come up; why germination is much easier
in soil that is mellow and can be permeated by the air than in soil
that is compact; why delicate seeds should be covered with very little
earth or even simply sown on the surface of the moist ground; and,
finally, why ground on being broken often becomes covered with fresh
vegetation from the sprouting of seeds that have for years lain dormant
in the soil, needing only to be stirred up and brought into contact
with the air in order to germinate.
“Under like conditions of temperature, moisture, and air, by no means
all seeds require the same length of time for germinating. Common
garden cress germinates in about two days. Spinach, turnips, and beans
take three days to come up; lettuce, four; melons and pumpkins, five;
cereals, about a week. Two years and sometimes more are needed by the
rose-bush, the hawthorn, and various stone-fruit trees. Generally seeds
with thick and hard shells are slow in germinating on account of the
obstacle they oppose to the penetration of moisture. Finally, when sown
fresh, immediately after coming to maturity, seeds germinate quicker
than when old, because old seeds have to recover by a prolonged sojourn
in the ground the moisture lost through prolonged drying.
“According to their kind, seeds retain for a longer or shorter period
their power of germinating; but why this vitality is more enduring in
one instance and less so in another, we cannot tell. Neither the bulk
of the seed nor the character of its outside coverings, nor the
presence or absence of a perisperm, appears to decide its longevity.
Such and such a seed lives for whole years, even centuries, while
another loses its germinating power in a few months, from no cause that
we can discover. Thus the seeds of the angelica will not come up unless
they are sown immediately after maturing; but beans have been known to
germinate after being kept more than a hundred years, and rye after a
hundred and forty. Excluded from the air, certain seeds may be kept for
centuries, always ready to germinate whenever favorable conditions
shall present themselves. This explains why strawberry, bluet, and
camomile seeds from ancient tombs have germinated just as new seeds
would have done. Finally, rush seeds have been made to germinate that
were dug up from great depths in the Island of the Seine, the original
site of Paris. Doubtless those seeds dated from the time when Paris,
under the name of Lutetia, consisted of a few mud and reed huts on the
marshy borders of the stream. But despite these remarkable exceptions
let us never forget that recent seed is preferable to old for sowing;
it comes up better and in greater abundance.
“We have just seen that certain seeds are very slow in coming up, as
for example the peach, apricot, and plum, whose thick shells resist the
moisture required for germination. Put directly into the ground in the
very places that the young plants are to occupy later, these seeds
would be exposed to not a few dangers during their leisurely
germination. Prolonged rains might make them rot; various marauders
that are partial to them, such as rats, field-mice, jays, magpies, and
crows, might dig them up and devour them. Besides, they would occupy
for a long time, with no profit to any one, the ground in which they
had been planted. All these objections are avoided by making a
preliminary planting after a method known as stratification, from the
Latin word stratum, meaning bed or layer. In a large, deep earthen pan,
with holes in its bottom, or in any other suitable receptacle, such as
a box, a pot, or a tub, likewise pierced with holes, it is the practice
to place first a layer of small pebbles. The holes at the bottom and
this layer of pebbles are to give easy access to the air and drain off
the excess of water after each irrigation. Next comes a bed of fine
sandy soil, then a layer or stratum of seeds arranged side by side, and
on top of that a second bed of earth. On this is placed another stratum
of seeds, which in its turn is covered with earth; and so the process
goes on with alternating layers of seeds and earth until the receptacle
is full. Then it is watered and placed in a cellar or a dark shed. All
that is necessary after this is to keep the contents of pan or tub
sufficiently moist by an occasional sprinkling. Enclosed thus in a
small space easy to watch over, with no danger from marauding animals,
and without needlessly occupying ground that might be used for other
purposes, the seeds can now take their own time to break their hard
shells and can germinate with all the slowness natural to them.
“When the shells at last crack open and the radicle appears, it is time
to proceed to the final planting. The half-germinated seeds are then
put into the ground one by one in an open field, each at the exact spot
the young plant is to occupy.
“Stratification offers still another advantage. Fruit trees as well as
other trees have a stout tap-root which bores vertically into the
ground to a considerable depth and gives a good deal of trouble if
transplanting is undertaken. To alter this tap-root into a root not
growing so deep, but branching horizontally, would be decidedly
advantageous. In speaking of the root we saw what the nursery-man does
to obtain this result. He passes the sharp edge of his spade under the
base of each tree-trunk so as to sever the tap-roots of his young
plantations. In stratification the method is much simpler and success
surer. With his thumb-nail the gardener nips off the tip of the tender
radicle before the final planting is done. That is all. Deprived of its
growing end the young root henceforth branches out horizontally instead
of descending vertically.”