27. THE EVERYDAY LIFE OF A GRASS.
1. =General features.=—Pull up a sod of couch grass or of Yorkshire
fog and clear away the earth as well as possible. Notice the fibrous,
creeping branches or _stolons_, and the bunches of fine roots. In
summer the plant sends up also erect branches called _haulms_, which
bear leaves and flowers. Examine the shape of the leaves and notice
their parallel venation, which indicates (p. 40) that the plant is a
monocotyledon.
Observe how the leaves are borne on the haulms. Each leaf arises at a
knot (node) which is slightly swollen. The first part of the leaf is
a _sheath_ which encloses the haulm up to perhaps the next knot. Then
the leaf-blade stands out from the haulm. Turn back the blade slightly
and notice at this point a little strap, the _ligule_ (Fig. 98), on the
upper surface of the leaf-blade. Notice the variation in the size and
shape of the ligules of different kinds of grass.
Pull the haulm until it gives way, and draw the broken part out of the
leaf-sheaths. Chew the end, and notice the taste of sugar. Cut across
haulms of various ages. The young haulms are solid; the old ones are
hollow except at the nodes, where there is a horizontal shelf. Notice
this also in a bamboo cane, which is the haulm of a large tropical
grass. In spring, mark a young haulm, so that you can recognise it, and
measure it day by day. Note the measurements made on various days, and
also the date of opening of the flowers.
2. =Different grasses.=—Learn to recognise different grasses, not only
by the way in which the clusters of flowers are borne on the haulms
(Figs. 102 to 110) and by their colours, but also by the general
appearance of the plant when it is not flowering; the size and shape of
the leaves, the character of the ligules, the manner of rooting, etc.
Again germinate grains of wheat, and especially notice the single
cotyledon, the leaves, and roots (p. 21).
=Importance of grasses.=—It is impossible to over-estimate the value
to man of the various grasses. From the earliest times he has obtained
his staple food from the grains of such cereals as wheat, barley,
oats, rice, and maize; and his flocks and herds have grazed upon the
nutritious herbage of the plains. The numberless applications of such
large tropical grasses as the bamboo and the sugar-cane are also
well known. Sugar occurs very generally in grasses. It can easily be
recognised even in ordinary meadow-grass by pulling out the upright
“stem” from the sheathing leaves, and chewing the tender end.
[Illustration: FIG. 98.—Part of a Grass Stem and Leaf. _h_, haulm;
_s_, part of leaf-blade; _l_, ligule; _v_, leaf-sheath; _k_, node-like
swelling at the base of the leaf-sheath. (× ½.).]
=The general characters of grasses.=—In this country, grasses are
usually herbs not more than three or four feet high. They have abundant
leaves, which are long, narrow, and pointed at the end; they have
parallel veins like the leaves of most other monocotyledons. The roots,
too, are of the usual monocotyledonous type—springing in bunches from
the base of the stem, not branching from a main tap-root. Most grasses
spread by prostrate creeping branches or =stolons= (p. 83), which
spring from the axils of leaves and then run along beneath the soil.
At some little distance from the parent shoot, the stolon forms roots
below and a new shoot above. Other stolons arise in the axils of the
leaves of the new shoots, and so the process is repeated. In this way
such grasses become thoroughly established in the soil, and—if they
are of the undesirable species which are classed as “weeds”—cause much
trouble. This habit of growth is, however, useful in binding together
the sand and earth of embankments, etc., into a compact mass. The new
shoots of stolon-bearing grasses are of two kinds. Throughout the
greater part of the year they consist of tufts of leaves; but, in the
spring and summer, there are also produced erect branches—commonly
known as stems, but better called =haulms=—which bear leaves in the
“alternate” manner. The point at which a leaf springs from the haulm is
called a knot or node; it is usually swollen. The distance between two
knots is, of course, an internode. Extra roots are often given off from
the lower nodes of the haulm.
The lowest part of the =leaf= is a cylindrical, and generally
split, sheath (Fig. 98), which closely embraces the haulm for some
distance—often for the length of an internode. The sheath protects and
supports the soft, growing internode, inside it. At the top of the
sheath is the blade of the leaf, which stands out from the haulm. At
the junction of the blade and sheath, on the upper surface of the leaf,
is a little membranous outgrowth called a =ligule= (Fig. 98, _l_). It
often varies greatly in size and shape in different species of grasses,
and is a valuable means of distinguishing between them. Its use is not
certainly known. The student should examine the ligule of every grass
he studies.
The haulm, or flowering branch, is for some time short and solid,
and its nodes are so close together that the sheath of a lower leaf
may overlap several upper leaves. The haulm is thus protected from
the rough weather of the early spring. In the meantime, the flowers
have been developing at its upper end. When they are almost ready to
open, the haulm begins to grow very rapidly; its internodes elongate
so quickly that the internal tissues are torn and the haulm becomes a
hollow straw, except at the nodes, where there are horizontal shelves.
The haulm hardens and stiffens as it grows, so that, when the spikelets
of flowers at its upper end open, they are carried high above the
leaves on a slender but very strong rod, which bends and dances in the
wind, and allows the pollen to be detached and blown to the stigmas of
other flowers.
28. THE REPRODUCTION OF A GRASS.
1. =The arrangement of the spikelets.=—Gather ears (flowering haulms)
of several different kinds of grasses and notice the arrangement of the
flowers. In the oat (Fig. 99), the meadow grasses (Fig. 103), fescues
(Fig. 102), and others, the nodding oval bodies, called _spikelets_,
are borne on delicate stalks which spread outwards from the haulm. In
the foxtails (Figs. 104 and 105), timothy (Fig. 106), and sweet vernal
grass (Fig. 110) the spikelets are on short stalks, which can, however,
be seen on bending the ear sharply on itself. In wheat, barley, couch
grass, rye, and rye grasses (Fig. 109) the spikelets are devoid of
stalks and are set close along the haulm. _Be quite sure you understand
what is meant by a spikelet._ 39 spikelets are shown in Fig. 99.
[Illustration: FIG. 99.—Panicle of Oats. (× ¼.)]
2. =The arrangement and structure of the flowers.=—Take an open
spikelet from the ear of a grass (_e.g._ oat) which has large flowers,
and examine it. At the bottom are two boat-shaped leaves—really
bracts—called _glumes_. Remove them carefully. Above them will be
found two or more flowers, each flower enclosed in two other leaves.
The outer of these two leaves is called the _outer pale_; the inner
is the _inner pale_. From the middle of the back of the outer pale of
the oat springs a bristle called an _awn_. Remove the outer pale and
make out the three _anthers_ on long filaments, and the ovary with two
branching feathery _stigmas_ and short styles. Fig. 100 is a diagram of
a spikelet, which makes clear the relation of the glumes, pales, and
flowers. Fig. 101, _A_, is a spikelet of meadow fescue. Its outer pales
differ from those of the oat in not bearing awns. Otherwise it is very
similar. Fig. 101, _B_, shows the appearance (magnified) of a flower
of meadow fescue from which the outer pale has been removed. The two
little scales seen in front of the ovary possibly represent a perianth.
Be careful not to confuse the terms ear, spikelet, and flower. The ear
consists of a number of spikelets, and each spikelet consists of glumes
and one or more flowers.
Similarly dissect spikelets and flowers of other grasses, making notes
of the lengths of the stalks of the spikelets, and the presence (and
lengths) or absence of awns.
3. =The use of the awns.=—Try to find out the use of the awns. Are they
generally rough or smooth? Have you ever seen grass “seeds” sticking in
the wool of sheep? What kept them attached?
4. =Grain.=—Examine several kinds of grass “seeds” and make out that
they not only consist of the entire ripened ovary and are therefore
_fruits_, but that usually the pales also remain attached to them.
5. =The embryo and endosperm.=—Again cut through soaked grains of maize
and wheat, and make out the embryo and endosperm (p. 19).
=Grass flowers.=—Grasses are true flowering plants; but because they
depend on the wind for the transference of pollen to the stigmas,
they do not pander to the taste of bees and butterflies by secreting
nectar, and hence have no need to display those advertisement placards
which we call petals. For this reason their flowers are not generally
recognised as such. It requires a little care to make out the parts
of the flower and to understand the manner in which the flowers are
arranged among themselves.
[Illustration: FIG. 100—Diagram of a Grass Spikelet. _g_, the glumes;
_p₁_ and _p₂_, the outer and inner pales; _B_, flower.]
The whole group of flowers borne by any one haulm is generally called
the =ear= or =panicle=. The ear in its turn consists of several bodies
called spikelets. The appearance of the ear varies greatly in different
grasses (Figs. 102 to 110) according as the stalks of the spikelets are
long and spread outwards from the haulm, as in the meadow-grasses (Fig.
103), oats (Figs. 99 and 108), fescues (Fig. 102), and others; short,
as in the foxtails (Figs. 104 and 105), timothy (Fig. 106), and sweet
vernal grass (Fig. 110); or absent altogether, as in the wheat, barley,
rye, rye grasses (Fig. 109), and couch grass.
A single =spikelet= of a grass is shown diagrammatically in Fig. 100.
At the bottom are two boat-shaped bracts called =glumes= (_g_, _g_),
which almost or entirely cover the spikelet before it opens. When the
glumes have been removed a few flowers remain. Each one is protected by
two leaves called =pales=: outer (_p₁_) and inner (_p₂_) respectively.
The flower (_B_), as a rule, has _three stamens_, the anthers being
borne on long filaments and dangling out to the wind (Fig. 101), and a
pistil with two branching feathery _stigmas_. In many grasses the outer
pale bears a bristle called an =awn=, well seen in “bearded” wheat,
barley, and upright brome grass.
Fig. 101, _A_, represents a single spikelet of meadow fescue, with two
open flowers. The outer pales of this grass are not awned. Fig. 101,
_B_, shows a single flower of the same grass from which the outer pale
has been removed. The two little scales seen in front of the ovary (and
at _e_ in Fig. 100) possibly represent all that is left of a perianth
(p. 121).
=Fertilisation.=—By the time the flowers have opened, the haulm has
usually grown so tall that they are lifted well above the leaves. The
stamens hang their anthers loosely out to the wind, and, as the slender
haulm sways in the breeze, the pollen is readily detached and carried
to other flowers, perhaps miles away.
It is in order to catch the wind-borne pollen-grains that the stigmas
of grasses are branched and feathery. A great waste of pollen is
obviously entailed by this method. But on the other hand it must
be remembered that insect-pollinated flowers have to pay for their
privileges by storing nectar in cunningly hidden pockets, and by
advertisement-expenses, all of which the grasses avoid.
[Illustration: FIG. 101.—Meadow Fescue. _A_, spikelet with two open
flowers (× 1½); _B_, a flower from which the outer pale has been
removed (× 6).]
The ovule is fertilised in the usual way, by a pollen tube growing down
the style from a grain on the stigma. As a result of fertilisation the
ovary becomes a fruit containing one seed which fills it. In many cases
(_e.g._ barley and oats) the pales still remain in position and adhere
to the fruit. When the awn is present it may play an important part in
distributing the “seeds” by clinging to the hides of animals, etc.
Sometimes the awn is of use in fixing the grain in position on the
ground until the seed has germinated.
The structure of a grass seed has already (p. 19) been studied in the
wheat and maize. The developing embryo (p. 21) lives upon a store of
food called the endosperm (Fig. 16) until its roots and leaves are
sufficiently advanced to make food for themselves.
29. SOME COMMON GRASSES.
1. =The fescues.=—Gather plants of _meadow fescue_, and examine the
habit of growth (in tufts), the broad leaves, and the nodding panicles
and the flowers. Also examine the “seeds.”
Compare _sheep’s fescue_ (Fig. 102), and notice the very fine leaves.
The outer pales are awned.
2. =The meadow grasses.=—Examine the various species of meadow grass
(Fig. 103). They can be distinguished from each other by the characters
of the ligules. Notice the tree-like habit of the panicles and compare
them with the fescues. The meadow grasses never bear awns. Notice the
woolly “webs” at the bases of the “seeds.”
3. =The foxtails.=—In _meadow foxtail_ (Fig. 104) notice the prostrate
stolons and large succulent leaves. Does the grass grow in tufts? Why
not? What is the earliest date on which you have seen it in flower?
Double the ear on itself to see the short stalks of the spikelets. How
many flowers are there in each spikelet? Notice the silky awns of the
flowers.
Compare the _slender foxtail_ (Fig. 105), which is a troublesome weed.
4. =Timothy.=—Compare the leaves and flowers of timothy or “meadow
catstail” (Fig. 106) with the meadow foxtail. The ear is green and
rough, and the flowers are awnless. What is the date of flowering?
5. =Yorkshire fog.=—Notice the woolly covering of this weed (Fig. 107).
This covering and its bitter flavour make it distasteful to cattle.
Observe the “kneed” awn of the flower. Dig up and shake off the earth
from a sod to see the stolons.
6. =Wild oat= (Fig. 108). Examine the large spikelets and make out the
long twisted awn of the flower. Compare this weed with the _cultivated
oat_ (Fig. 99) and with the _yellow oat grass_.
7. =The perennial rye grass.=—Notice that the ear is flattened, and
that the spikelets are without stalks and have only one glume. The leaf
is glossy and has a prominent midrib and a flattened sheath.
[Illustration: FIG. 102.—Sheep’s Fescue. (× ⅙.)]
[Illustration: FIG. 103.—Smooth-stalked Meadow Grass. (× ⅙.)]
8. =Sweet-scented vernal grass.=—Notice the tufted habit of growth
and the characters of the leaves. Chew the stalk and notice the sweet
odour of new-mown hay. What is the date of flowering? Make out that the
flower has two stamens only.
9. =Rushes and sedges.=—Rushes and sedges are sometimes mistaken for
grasses. Examine the stems, the flowers, and the leaves (look for
ligules), and tabulate as many differences from the true grasses as
possible.
The student should learn to recognise the common grasses and to
distinguish the useful species from the weeds. When the grasses are in
flower there is not much difficulty in doing this, but the habit of
growth—the characters of the leaves and roots, and of the stolons of
the perennial species—should also be noticed carefully, as during the
greater part of the year these alone can be depended upon.
[Illustration: FIG. 104.—Meadow Foxtail. (× ⅙.)]
[Illustration: FIG. 105.—Slender Foxtail. (× ⅙.)]
=The fescues= fall into two groups according as their leaves are broad
or narrow. The =meadow fescue= is a good example of the former group.
It is found in meadows and pastures and has long broad leaves. =Sheep’s
fescue= (Fig. 102) is a good example of the second group of fescues.
It has very fine—almost bristle-shaped—leaves. Like the meadow fescue
it grows in tufts; it inhabits high lands and downs, especially in
limestone districts. The nodding spikelets are borne on fairly long
stalks, and the panicles are somewhat like those of the meadow grasses
(Fig. 103). The flowers of sheep’s fescue, however, bear short awns.
=The meadow grasses= much resemble the fescues in general appearance,
but the panicles (Fig. 103) are rather more tree-like—the stalks of the
spikelets spreading more horizontally—and the flowers are never awned.
The various species can be distinguished by their ligules; for example,
the ligule of the =smooth-stalked meadow grass= (Fig. 103) is blunt,
while that of the =rough-stalked= species is long and pointed. The
=annual meadow grass= is a weed to be found almost everywhere.
[Illustration: FIG. 106.—Timothy Grass. (× ⅙.)]
=The foxtails= are easily recognised by the tail-like appearance of the
ears (Figs. 104 and 105). The =meadow foxtail= (Fig. 104) is a valuable
grass with broad, long, and succulent leaves. It spreads by means of
prostrate stolons. The spikelets have short stalks, as can be seen on
bending the ear on itself, and each spikelet contains only one flower.
The silky awns give the ear a silvery grey colour. The grass flowers in
early spring. The =slender foxtail= (Fig. 105) is a most injurious weed
of cornfields. It can be distinguished from the meadow foxtail by its
less vigorous appearance, by the thinner and more pointed ear, and by
the black patches on the ear. It is often called “black bent.”
=Timothy grass= or “meadow catstail” (Fig. 106) has a general
resemblance to meadow foxtail, but its ears are rough to the touch and
green in colour. It also flowers much later in the year (July) and its
pales are awnless; the two grasses are therefore easily distinguished.
Timothy grows abundantly in clay soils, forming fairly close tufts.
[Illustration: FIG. 107.—Yorkshire Fog. (× ⅙.)]
[Illustration: FIG. 108.—Wild Oat. (× ⅙.)]
=Yorkshire fog= (Fig. 107) is a rank weed which is distasteful to
cattle, partly because it is covered with hairs and is difficult to
wet, and partly because it has a bitter flavour. It is pale in colour
and soft. It spreads rapidly by means of creeping stolons.
=Oat= grasses are of several species; one is cultivated as a cereal,
others are valued as forage for cattle, while others still are
troublesome weeds. The =wild oat= (Fig. 108) is a common weed in
cornfields. It is an annual, from two or three feet high, with large
spikelets forming a loose panicle, the flowers having awns twice as
long as the spikelets. The cultivated oat is supposed to be a variety
of the wild oat. The panicle of the =yellow oat grass= is oblong, and
has erect spikelets.
[Illustration: FIG. 109.—Perennial Rye Grass. (× ⅙.)]
[Illustration: FIG. 110.—Sweet-scented Vernal Grass. (× ⅙.)]
The =perennial rye grass= (Fig. 109) is very easily recognised by
its flattened ears of alternate, stalkless spikelets. Each spikelet
has only one glume. The leaves are dark-green and glossy, and the
leaf-sheaths are flattened instead of being round, as is the case with
most grasses. This is one of the most valuable of forage grasses.
=Sweet-scented vernal grass= (Fig. 110) does not occur very abundantly
in meadows and pastures, but the fragrance of new-mown hay is almost
wholly attributed to it. The odour can be distinctly perceived when a
stalk of the grass is chewed. The leaves are somewhat hairy and are
broad and flat. The spikelets are borne on short stalks. The flowers
open early and are remarkable in possessing only two stamens instead of
three.
=Rushes= and =sedges= are monocotyledonous plants which are often
erroneously called grasses. The stems of =rushes= are vivid green,
round, and pointed, and contain a distinct pith. The flowers (Fig.
111) are never in spikelets; they contain six stamens, and the pistil
has three long stigmas. The =sedges=, like grasses, have narrow,
pointed leaves, but the ligules are either very small or absent, and
the leaf-sheaths are not split. The flowers are often in spikelets
with glumes, as are grass flowers. The stems of sedges are solid and
triangular.
[Illustration: FIG. 111.—A Rush. _a_, flowering part of stem; single
flower (_b_) and pistil (_c_) more highly magnified.]
The flowers of rushes in many respects resemble those of the lily
family. Indeed it is supposed that the ancestors, not only of the lily
family, but also (along a different line) of the grasses and sedges,
were primitive and now extinct rushes. The lilies have developed the
rush perianth more and more as they have increasingly depended on
insects for pollination; while in the grasses and sedges the perianth
has gradually dwindled because these plants found that wind-pollination
was sufficient for their needs.
EXERCISES ON CHAPTER VII.
1. What grasses are grown as corn in your part of the
country? How can you recognise the grasses (_a_) before
flowering, (_b_) in the ear, (_c_) by the straw?
2. What forage grasses are most cultivated in your part of
the country? Make a list of the earliest dates on which
you have seen each in flower.
3. Examine grains of wheat, barley, oats, and rye, as
harvested. In which of these are the pales present? What
is the “beard” of barley?
4. Make a collection of “seeds” of various grasses,
and write down the characters by which they may be
distinguished from each other.
5. What are the commonest weeds you have seen in corn
fields? Do the corn and the weeds flower at the same time
or not? Is the time of flowering an advantage (_a_) to the
weeds, (_b_) to the farmer?
6. In what important respects do wind-fertilized flowers
differ from insect-fertilized flowers? Give examples of
each. (1898)