We all know, in a general way, that nothing grows unless it is alive,
and yet who ever thinks of bread dough as having life in it? There never
was a garden bed so full of living plants as is the loaf when it is
moulded into shape, and ready to be put into the oven. If you have never
watched the mixing of bread, I would advise you to go and look at it the
first chance you have, for it is a very curious and entertaining bit of
gardening. The cook first prepares her seed, which is the yeast. There
are several ways of planting yeast, as there are of planting other seed.
You may either soak it to make the seed sprout quickly, or you may start
the little plants in a hot-bed, or, again, you may buy your young
seedlings, and transplant them into your own garden plot. Just so you
may get your yeast seed ready to plant. The yeast cake may be only
melted in warm water, or it may be set to start in a cup of water and
flour by the warm kitchen fire, or you may buy the yeast already grown
at the baker's.
When the seed or seedlings are ready, the garden plot is prepared. The
cook heaps up in her bread bowl quarts of snowy flour. Into this heap,
after making a hole, she pours her prepared yeast. Working the bread is
only another name for the careful scattering of the seed through all the
dough, that it may spring up and grow, and fill the whole mass with the
tiny plants.
[Illustration: FIG. 1--TOAD-STOOLS.]
The yeast plant is not a common kind of plant, but belongs to the same
class as mushrooms and toad-stools, and the fuzzy, cottony growth that
we call mould. There are two kinds of plants that we may find almost
anywhere in the fields and woods, and even in the city yards--the fungi
and the green plants. The yeast plant is one of the fungi. These are
very different in most respects from the green plants: they can live and
grow and thrive in darkness; they do not have either leaves or flowers,
and they usually spring up and die very quickly. The greatest real
difference between the two kinds is, however, that the fungi live on
food that has been alive before--on plants, or animals, or decaying
matter, while the green plants live on what they get out of the earth
and the air and the water.
[Illustration: FIG. 2.--YEAST PLANT.
_a_, Single cells; _b_, growing plants.]
The simplest of all the fungi is the yeast plant. It begins its life as
a tiny egg-shaped bag, or sac (Fig. 2 _a_). This cell, as it is called,
is filled with a very curious jelly, perhaps the most wonderful thing in
all the world. It is found in everything that lives and grows. By its
help the little yeast plant can take the flour and water, and can change
it so that while the paste is used up and disappears, the cells grow
larger, and sprout out buds. You have particles of this jelly, or
_protoplasm_, lining your mouth and stomach, and the food you eat is
changed into flesh and blood and bones by this wonder-working magician.
In the figures, the grainy substance is the protoplasm.
This jelly all seems to be pretty much alike, but there is some
marvellous difference somewhere--a difference that science has never
reached. The yeast cell takes in certain food, and grows, but it never
makes anything but other or larger yeast cells. The food you eat and
digest makes just _you_; more of you, perhaps, but still you, yourself,
and nobody else.
[Illustration: FIG. 3.--MOULD.]
Like all living things, the tiny yeast cell must eat and breathe, or it
will die. It feeds, not by opening its mouth and taking in its food, but
by lying bathed in it, and soaking it up through its skin. When the cook
dissolves her yeast cake, and puts it into the spongy dough, she is
putting the little plant into its food bath. The cells which have been
so long in prison, shut up in the darkness and cold of the dried yeast,
begin to look alive, and stretch themselves, and enjoy their liberty.
They take kindly to their food right away, and begin helping themselves
to what they find about them. They do not merely soak up the flour and
water in which they are plunged, but they manage to extract from the
compound just what they need.
The cells must not only feed in order to live, but they must breathe,
they must somehow get oxygen, which is the gas that our breathing takes
out of the air. And this they extract, as a miner does gold, by
separating it from its ore. There is a certain amount of sugar in wheat,
which gives to good bread and to cracked wheat their delicate sweetness
of flavor. Sugar is made up of a number of different substances, which
the yeast cell has the power of separating. It takes the oxygen for its
own use, and leaves behind the other things that make up the sugar.
Feeding and breathing in this way, by taking what it needs from the
flour, the cell grows. When it has reached its mature size, it rests
quietly for a while as if it were gathering strength for the effort, and
then it sends out a little bud, which grows like the parent cell, until
another bud and another grow from it. When the plant is grown, it is
very unlike our notion of a plant; it is really nothing more than a
little chain of sacs growing end to end. As soon as the little plant has
exhausted all the sugar and food substance of the flour, it stops
growing, the cells separate, and remain quite still.
There is just one time in the growth of the plant when the dough is
right for baking. Before it has grown enough, the bubbles through the
dough are too few or too small. These bubbles are the carbonic acid gas
left behind when the oxygen has been taken out of the sugar, and there
must be plenty of them to make the bread light. If the bread is left too
long to rise, the cells get more than their share of the wheat sugar,
and the bread is sour. Just at the right stage, which every good
bread-maker can tell by experience, a thorough baking will destroy the
alcohol, and the bread will be both sweet and light.
When the yeast plant is sowed on the top of the flour and water, instead
of being buried in it, all this is very different. The plant takes its
food from the paste, but it does not need the sugar, so it lets that
alone. It can get its oxygen in a much simpler way, right from the air,
as we do, and does not need to go through the labor of smelting it out
of the sugar. The raising of our bread by yeast is entirely due to the
efforts of the tiny cells to get a breath of air when we have smothered
them up in the dough.
There are other plants besides the yeast plant that act in the same way.
Have you never heard your mother say, when she opened a jar of
preserves, "These are all right, I know, for they are covered with
mould"? Mould is a good deal like yeast in some things; if the germ
cell, or spore, falls upon the top of the sweetmeats, it can get plenty
of oxygen from the air, and so lets the sugar alone. But if it is nearly
drowned in the syrup, it will get its oxygen somehow, and so the sugar
has to be sacrificed, and the preserves are left to spoil. What else
could you expect of such little mischief-makers if you shut them up with
the sweetmeats?
The yeast plant is so very, very small that you can not see it except
with a very fine magnifying glass. But there are other plants like it
which are large enough to be seen with a small and not a costly
microscope.[2] These are what we call moulds. If you want to study
moulds, nothing is easier than to prepare them. Mix a spoonful of flour
with cold water, and spread the paste over the bottom of a plate or
saucer. In a few days it will be covered all over. If you put it in a
damp and dark place, the mould will sprout sooner. You might put away a
piece of bread at the same time, and you will find it covered with a
growth too.
[2] There is a little microscope which I find in Queen's Catalogue,
called the Excelsior, No. 3050, price $2.75, with three lenses. This I
have used, and found very good. It is in a small walnut box 3 by 1-3/8
inches in size, having a little mirror, stand, and two dissecting
needles. It magnifies about twelve diameters (nearly 150 times in area),
and gives a good clear image, besides having the advantage of being an
excellent pocket glass, even if you should buy a more costly instrument
hereafter.
[Illustration: FIG. 4.--MOULD.
_a_, Rosette Heads; _b_, Fruit.]
Take a bit of this paste on the blade of a knife, and examine it
carefully. You will see among the cottony fibres a number of little
upright stems with black or white or yellow heads, which give the mould
a speckled look. Under the microscope you see a perfect jungle of
growth--a tangle of threads, which look like spun glass, running here
and there and everywhere. From these, which are the roots of the mould,
the stems spring up, bearing, instead of leaves or flowers, tiny
glistening toad-stools that look as if they were made out of a pearl; or
sometimes the heads are like strings of little pearls (Fig. 3), or at
others they are rosettes of such strings (Fig. 4 _a_). The black and
sage green colors come later, and are the fruit or seed-bearing portion
of the plant (Fig. 4 _b_).
[Illustration: FIG. 5.--MOULD.
_a_, Stalk; _b_, same opened; _c_, outer skin broken, and spores
scattering.]
On my saucer of paste I found in one place a plantation of delicate
yellow fungi. The stems came up thick, with the little round fruit at
the end of each, looking as if the whole thing was carved out of amber.
In another place, over the yawning caverns made by the cracks in the
paste, there were delicate forms like grasses in seed, all looking like
spun glass. The largest kind of common mould, which you may see in Fig.
5, is not so beautiful as these I have just described, but it shows very
well the way the fungi grow, and form their seed, and then sow
themselves. This plant is easily seen without any microscope, but looked
at through the little Excelsior glass, you see a great deal more. The
stalks look as they do in Fig. 5 _a_. If you are so fortunate as to have
a large microscope, and watch them from day to day, you will see them
look as they do in Fig. 5 _b_, and finally, when the outer skin breaks,
like _c_, in the same illustration.
A single spoonful of flour will give you this wonderful garden, with its
crop of yeast plant, if you sow the seed, or, if you trust to luck, its
harvest of chance-sown mould. The air is full of these spores of the
mould plants, and wherever they find a place they will take possession
of it, and grow up without planting or cultivating, as weeds do. You can
be certain of your yeast crop, because you have sowed it; but you must
take your chances with the mould. You are almost sure, however, to find
in any saucer of paste the different kinds described and pictured in
Figs. 3, 4, and 5.
It is worth while sometimes to get away from the every-day world, and
learn the wonders that are to be found in the fairy ring to which the
microscope admits us.