15. A TYPICAL FLOWER.
=I. The wallflower.=—After noticing the general habit of growth of a
wallflower plant (Fig. 57), and especially the shape and venation of
the leaves, make out the following parts in one of its flowers. On the
top of the flower-stalk (called the _receptacle_) are:
[Illustration: FIG. 57.—Wallflower. (× ⅙.)]
(_a_) Four small, narrow, purplish leaves, called _sepals_. The four
sepals together constitute the _calyx_. Take off the sepals one by one.
Notice that two opposite sepals are bulged out at their bases, forming
pouches containing nectar. Try to get out a small drop of nectar on the
point of a pencil and taste it.
(_b_) Four showy leaves arranged in the form of a Maltese cross,
called _petals_. They are yellow, or red, or purplish in colour, are
delicately scented, and have beautiful velvety surfaces. The four
petals together constitute the _corolla_. Take off the petals one by
one.
(_c_) Six _stamens_, each consisting of a greenish stalk or _filament_
surmounted by a yellow, boat-shaped body, called the _anther_. The
anther is a four-chambered box containing an enormous number of tiny
yellow grains called _pollen grains_. Two of the stamens are shorter,
and are fixed at a lower level on the receptacle than the remaining
four. Take off the stamens one by one.
(_d_) A central _pistil_, shaped somewhat like a slender bottle. At
the top, where the cork would come in a real bottle, is the notched
_stigma_, slightly sticky. The neck is called the _style_, and the part
corresponding to the body of the bottle is the _ovary_. Tear open the
ovary with a needle to see the _ovules_, which in an undisturbed flower
would have become seeds.
Watch bees visiting flowers. Does each bee confine itself to one kind
(species) of flower at each journey, or does it visit several kinds
indiscriminately? Try to discover what the bees are doing. Avoid
alarming them.
=The work of flowers.=—The roots, stem, and leaves of a plant do a
great deal of work, but, as it is performed for the benefit of the
plant itself, it is all, in a sense, selfish work. Plants, however,
like animals, grow old in time, and at last die. If they are not to
become extinct it is evident that they must devote part of their
energies to producing new individuals, and to sending these forth into
the world as well equipped as possible for the battle of life. This
unselfish and self-sacrificing part of a plant’s life-work is called
=reproduction=; in the higher plants it is carried out by flowers.
=The structure of a wallflower blossom.=—The flowers of different
groups of plants vary greatly in structure, but a good general idea of
the arrangement of the parts of a flower can be obtained by examining
the blossoms of a wallflower plant (Fig. 58). Other flowers may
afterwards be compared and contrasted.
[Illustration: FIG. 58.—Wallflower. _A_, branch, bearing leaves and
flowers; _B_, flower; _C_, longitudinal section of flower; _D_, stamens
and pistil; _E_, fruit; _S_, transverse section of stem, (× ½.)]
There are evidently at least eight leaves in the flower, but, unlike
the green foliage leaves, these are not arranged spirally, but stand
at nearly the same level on the end—called the =receptacle=—of the
flower-stalk. The most external leaves are four in number, small,
narrow, and purplish in colour. Each of these leaves is called a
=sepal=, and the four sepals together constitute the =calyx= of the
flower. Two opposite sepals are pouched at the base, forming pockets,
in which a sugary fluid, called nectar, collects. Before the bud
opens, the calyx is the only part of the flower which is visible. It
is probably developed in the wallflower solely for the protection of
the more delicate structures within. Next, inside the sepals, placed
alternately with them, and standing a little higher on the receptacle,
are four showy leaves arranged in the form of a Maltese cross. These
leaves are called =petals=, and the four petals together form the
=corolla=. The petals are delicately scented, and their surfaces have a
beautiful velvety sheen.
[Illustration: FIG. 59.—Cross section through a Wallflower bud. _Sep_,
sepals; _Pet_, petals; _lg.st._, anther of a long stamen; _sh. st._,
anther of a short stamen; _pol.sac._, pollen sacs; _Ov_, wall of ovary;
_Ovl_, ovule. (× 8.)]
When the sepals and petals are removed, there remain standing on the
receptacle six =stamens= surrounding a centrally-placed =pistil=
(Fig. 58, D). The stamens are the male part, and the pistil is the
female part, of the flower. Each stamen consists of a greenish stalk
or =filament=, surmounted by a yellow boat-shaped body called the
=anther=. The anther is a box with four compartments (Fig. 59). When it
is ripe, each compartment contains an enormous number of tiny, yellow
grains called =pollen grains=; and when the anther bursts (as it does
as soon as the flower opens) its inner face is covered by the yellow
dust of the pollen.
The =pistil= bears a rough resemblance to a slender bottle, and
consists of three distinct parts. The neck of the “bottle,” called
the =style=, is short in the wallflower, and differs from an ordinary
bottle-neck in being solid instead of tubular. At the top of the neck,
where the cork would come in a real bottle, is a body called the
=stigma=. The stigma of the wallflower pistil is hairy, notched, and
slightly sticky, from the presence of a sugary solution which forms
upon it. The part of the pistil, corresponding to the body of the
bottle, is the =ovary=. It contains four rows of little white =ovules=,
which are destined to become seeds capable of growing up and forming
new wallflower plants.
The relations of the parts of the flower are well seen in Fig. 59.
=Fertilisation.=—In order that an ovule may become a seed, its contents
must mix with the contents of a pollen grain. The fusion of the two
constitutes =fertilisation=. For fertilisation to take place, the
pollen grain must first of all gain access to the stigma of the pistil.
If this be prevented the flowers will wither without forming ripe
seeds. (This may be proved easily by Expts. =18=, 3 and =21=, 2.) The
sugary solution at the top of the stigma stimulates the pollen grains
to growth, and each puts out a long tube which grows down the style.
The living matter of the grains keeps near the tips of the tubes as
these continue their journey down the style. At length the tubes enter
the ovary and find the ovules. Each ovule has at one end a minute pore
(the micropyle—p. 6), and a pollen tube finds this and enters it. The
living matter of the pollen tube fuses with that of the ovule in the
neighbourhood of the pore, and fertilisation is effected. It is now
easy to understand that the comparatively insignificant stamens and
pistil are the all-important parts of a flower.
=How the wallflower advertises.=—Botanists have proved that a flower
produces more, and also better, seeds when it is fertilised by pollen
from another flower of the same species. This is called =cross
fertilisation=. The wallflower relies upon bees for the transference of
the pollen from one flower to another; and it is solely to attract them
that the petals are so delicately scented and brilliantly coloured, and
that sweet nectar collects in the sepal-pouches. The gaily coloured
petals are therefore advertisement placards which are hung out to
attract the attention of bees. A bee comes to a wallflower for the
sake of both nectar and pollen—the “bee-bread.” As the bee thrusts its
proboscis down between stamens and pistil in search of the sweet liquid
in the pouches, its head is pretty certain to come in contact with,
and to brush off, some of the pollen dust hanging loose on the inner
faces of the anthers. When the bee flies off to another wallflower and
continues its search for nectar, it almost invariably leaves some of
the pollen, from the first flower, on the hairy and sticky stigma of
the second.
In almost all cases when a flower is brightly coloured it depends upon
the help of insects for cross fertilisation.
16. THE WALLFLOWER FAMILY.
[Illustration: FIG. 60.—Shepherd’s Purse. (× ½.)]
1. =Shepherd’s purse.=—Compare the shepherd’s purse (Fig. 60) with the
wallflower. The flower is very much smaller, and white, but the parts
have the same arrangement as in the wallflower, viz., four sepals,
four petals arranged in the form of a cross, six stamens (two short
and four long), and a central pistil, all arranged separately on the
receptacle. Look down the plant, and notice that in the oldest (lowest)
flowers, everything but the pistil has dropped off, and that this
has become greatly enlarged to form a _fruit_. Cut some fruits open,
both lengthwise and crosswise, and observe that each consists of two
pocket-like chambers, separated by a thin partition on which the seeds
are borne. Notice the manner in which the oldest fruits have opened
naturally.
2. =Other relatives of the wallflower.=—Compare also the flowers and
fruits of the stock and candytuft, and also cress, mustard, radish
(Fig. 61), cabbage, and turnip, which have been allowed to “run to
seed.” Examine the roots of the turnip and radish.
Make a note of the earliest dates on which you see the above plants in
flower.
=The wallflower family.=—The plants of the family to which the
wallflower belongs are of very great importance to mankind; for
while not one of them is poisonous, many are extremely valuable as
food-crops. They are all _dicotyledons_; that is, their seeds contain
two cotyledons or “makeshift leaves,” as has already (Chapter I.)
been seen in the case of the mustard. The net-like venation of the
leaves of the full-grown plant also indicates this. There is a great
family likeness between the flowers of this group, and they are easily
recognised (Fig. 61 _a_, _c_) by the cross-shaped corolla and the six
stamens (two short and four long). All the parts of the flower—sepals,
petals, stamens, and pistil—are fixed separately on the top of the
flower stalk or receptacle. The cross-arrangement of the petals has
led to these plants being called =Crucifers= (cross-bearers). The
=shepherd’s purse= (Fig. 60)—so-called from the shape of its fruit—is
a common weed with small, white flowers. All stages of the flower may
generally be found on the same plant. While at the top the buds may
still be unopened, the flowers below have been fertilised (in this case
generally self-fertilised); the sepals, petals, and stamens—having
fulfilled their duties—have fallen off; the ovules have become seeds,
and the ovule-box or ovary has become a seed-box or fruit, consisting
of two bags separated by a partition which bears two rows of seeds on
each side (Fig. 62).
[Illustration: FIG. 61.—Wild Radish. _a_, flower (nat. size); _b_,
petal; _c_, stamens and pistil (× 2); _d_, pistil (× 2); _e_, fruit (×
1); _f_, cross section of fruit; _g_ and _h_, embryo (mag.)]
[Illustration: FIG. 62.—_A_, Fruits of Shepherd’s Purse (× ½); _B_, a
single open fruit (mag.); _C_, cross section of _B_.]
[Illustration: FIG. 63.—Root of Turnip. (× ⅓.)]
[Illustration: FIG. 64.—Root of Radish. (× ½.)]
=Useful crucifers.=—The turnip and the radish are largely cultivated
for their roots (Figs. 63 and 64), and are then taken out of the
ground at the end of their first season. As these plants naturally
flower in their second year of growth and then die, they are called
=biennials=. The production of flowers and fruit is a great strain on a
plant, and it is to prepare for the effort that the turnip and radish
store so much food in their roots during the first year as to give them
a globular and spindle shape respectively. A carrot is not a crucifer,
but it also adopts this device.
The cabbage is grown for its leaves. Varieties of the cabbage are
Brussels sprouts, broccoli, and cauliflower; it is the very small
flower-buds of the last two which are eaten. Cress and white mustard
are eaten in the seedling stage. The seeds of the black mustard are
ground and eaten as a condiment.
17. THE BUTTERCUP FAMILY.
1. =The buttercup.=—Notice the habit of growth, characters of the
leaves, etc. Is the buttercup a dicotyledon? Make this observation with
all flowering plants. (See, however, Chap. VIII., p. 163.)
In the flowers of a buttercup (Fig. 65) make out:
(_a_) The _calyx_ of five green, separate sepals; they are
the only parts to be seen in young, unopened buds. Take off
the sepals of a fully-opened flower one by one.
(_b_) The _corolla_ of five, golden-yellow, separate
petals, alternate with the sepals. Notice the nectary—a
little pocket—near the base of the upper surface of each
petal. Take off the petals one by one and observe that they
are fixed on the receptacle, a little higher than the sepals.
(_c_) The large number of separate _stamens_, inserted
still higher on the receptacle.
(_d_) On the top of the receptacle the large number of
separate, flask-shaped bodies, which together make up the
_pistil_. Each of these is called a _carpel_.
Watch bees and other insects visiting buttercups and notice how they
stand on the flower to obtain the nectar from the nectaries. Does a bee
on leaving go to another buttercup, or does it change to another kind
of flower?
In a flower from which the sepals, petals, and stamens have fallen,
notice the compound _fruit_ (Fig. 66), consisting of ripened carpels.
Open a carpel with a needle and pick out the single seed.
2. =Other plants of the buttercup family.=—Notice that in the anemone
(Fig. 67) and marsh marigold (Fig. 68), the sepals appear to be absent
(the three leaves under the anemone flower are not parts of the flower;
they are called _bracts_). The apparent petals are really the sepals;
it is the corolla which is absent. Observe the large number of stamens,
and notice that the pistil consists of several separate carpels.
In what kind of ground have you seen these plants growing wild?
[Illustration: FIG. 65.—Buttercup. (× ¹/₁₀.)]
=The buttercup family.=—The buttercup (Fig. 65) and its relatives
resemble the crucifers (1) in being dicotyledons (as is indicated (p.
40) by the venation of the leaves), and (2) in the fact that, of the
parts which compose the flower, each group is arranged separately on
the receptacle. For example, the stamens are not connected with either
the calyx, the corolla or the pistil. Having noted these points of
resemblance, however, we are met by some important differences. In the
buttercup there are usually five sepals and five petals; there may
be twenty or more stamens; and the pistil is not a single structure,
but consists of a number of separate parts, each of which is called
a =carpel=, and contains a single ovule. The pistil of a crucifer
consists of only two carpels; these are welded together into a single
structure, and until the fruit ripens a slight notch in the stigma is
the only external indication that the pistil is in two parts.
[Illustration: FIG. 66.—_a_, Compound fruit of Buttercup (× 2½); _b_, a
carpel (× 4); _c_, carpel in longitudinal section (× 4).]
[Illustration: FIG. 67.—Anemone. (× ⅓.)]
Insects visit buttercups for the sake of nectar and pollen, and whilst
creeping about the flower transfer pollen to the stigmas of the
carpels. The insects may have brought some of this pollen from other
flowers, and then cross-fertilisation is caused. If the pollen is
derived from the same flower self-fertilisation is the result.
After fertilisation the ovules become seeds; the sepals, petals, and
stamens drop off; and the carpels swell up, forming a dry compound
fruit (Fig. 66), consisting of several nutlets.
Two other common plants of this family are the =anemone= (Fig. 67) and
=marsh marigold= (Fig. 68). In neither of these cases has the flower
any petals, but the calyx has taken on the appearance of a corolla. In
the marsh marigold it is large and yellow; in the anemone it is white
or purple. The three green leaves immediately beneath the flower of the
anemone are called _bracts_. They should not be mistaken for sepals.
[Illustration: FIG. 68.—Marsh Marigold. (× ⅙.)]
The plants of the buttercup family are as generally poisonous as the
crucifers are wholesome. Monkshood is especially poisonous, and its
root has been mistaken, with fatal results, for that of horse-radish.
It is often noticed that grazing cattle avoid the buttercups in a
field. The bitter and disagreeable taste of the leaves is of course a
valuable protection to the plant.
18. THE PEA FAMILY.
1. =The garden pea.=—Notice again the habit of the plant: its compound,
net-veined leaves with large stipules, and its method of climbing by
tendrils which are modified leaflets. Examine the flower and make out
(_a_) the _calyx_ of five united sepals; (_b_) the curiously shaped
_corolla_. The large upper petal is called the _standard_, the two at
the side are the _wings_, and the lowest (really two locked together)
is the _keel_; (_c_) the ten _stamens_. One (opposite the standard) is
separate; the remaining nine have the lower parts of their filaments
united to form a tube. Slit open the filament-tube and remove the
stamens, noticing how they are attached to the other parts of the
flower; (_d_) the _pistil_. Slit open the ovary and see the ovules in
it. Watch the various stages of the formation of the fruit (pod).
[Illustration: FIG. 69.—Vetch. (× ⅓.)]
Watch bees visiting the flowers. The insect alights on the wings, and
its weight pulls them down and lowers the keel, bringing the stamens
against the bee’s body.
Cut a complete flower down the middle with a sharp knife, and notice
that calyx, corolla, and stamens seem not to be inserted separately on
the receptacle, but to spring from a common base.
2. =Other plants of the pea family.=—Examine also bean, vetch (Fig.
69), meadow vetchling (Fig. 70), clover (Fig. 71), laburnum (Fig. 73),
and broom. Compare the habits of growth of the plants, and notice that
they all have the same peculiar shape of flower. Dissect a flower of
each. Notice that in laburnum and broom the ten stamens are all united.
In clover the flowers are in _heads_. Notice how the leaflets of the
clover plant close at sunset.
3. =Fertilisation.=—Dig up several red clover plants in early summer
and pot them. Cover about half the plants with gauze, so fixed on wire
frames that insects cannot get inside, and then put all the plants
together where they will get plenty of sun. Water them regularly, and
notice which plants ripen seed. How do you account for the differences?
[Illustration: FIG. 70.—Meadow Vetchling. (× ¼.)]
[Illustration: FIG. 71.—Red Clover. (× ⅙.)]
[Illustration: FIG. 72.—Bird’s-foot Trefoil. 1, flowering branch (× ⅔);
2, flower; 3, pistil and stamens; 4, pistil (× 1¹/₉); 5, fruit (× ⅔); 6,
corolla; _a_, standard; _b_, wings; _c_, keel; 7, diagram of flower.]
[Illustration: FIG. 73.—Flowering branch of Laburnum; _st_, standard;
_w_, wings; _k_, keel; 1, 2, 3, the flower from different points of
view. (× ½.)]
=The pea family.=—Plants of the pea family are found in all quarters
of the earth. They are of very diverse size and habit of growth; the
laburnum, for example, is a tree; the gorse is a bush; the broad
bean has a strong, erect, herbaceous stem; the pea is a weak-stemmed
climbing plant; the clovers are small herbs with flowers forming
“heads.” Most of the members of the family agree in having a
“butterfly-shaped” corolla (Figs. 72 and 73), which consists of three
well-marked parts, viz., a large =standard=, a pair of =wings=, and two
closely-connected petals which form a boat-shaped =keel=. There are ten
stamens, and the filaments of nine of these usually cohere to form a
tube surrounding the ovary. In the laburnum, gorse, and a few others,
all the ten stamens are united. When a bee visits the flower, in search
of nectar, it alights on the “wings” of the flower, and its weight
depresses these and pulls down the keel. The anthers of the stamens
are so placed with respect to the keel that this results in a mass of
pollen being scraped off the anthers and forced out at the beak of the
keel, or in the stamens being suddenly liberated and scattering pollen
on the bee. The pollen sticks to the bee’s body, and some of it is
almost certainly transferred to the stigma of the next flower visited.
The quaint shape of the corolla is thus definitely adapted to the
visits of insects; for the nectar is so placed that to obtain it the
insect must carry off some of the pollen.
The calyx, corolla, and stamens are not obviously—as in the wallflower
and buttercup—inserted separately on the receptacle, but seem to spring
from a common base.
The fruit is a =pod= (Fig. 3), which opens when ripe along both margins
and liberates the seeds. Laburnum seeds are poisonous, but the seeds
of many other plants of the family (peas, beans, lentils, etc.) are
valuable foods.
19. THE ROSE FAMILY.
1. =The wild rose= (Fig. 75).—With a sharp knife cut vertically through
the middle of a wild rose. Notice that the receptacle forms a deep
cup, and that the carpels of the pistil are enclosed in the cup. From
the edge of the cup spring the five sepals, five petals, and numerous
stamens. What is the great difference between a rose and a buttercup?
Trace the formation of the succulent fruit or hip from the receptacle
cup of the flower. Cut through a rose hip, and observe the ripened
carpels in the interior.
2. =The blackberry.=—Similarly examine a blackberry flower (Fig. 76).
This is still more like a buttercup, but—as in the rose and the pea—the
calyx, corolla, and stamens seem to spring from a common base, and not
to be inserted separately on the receptacle.
Trace the formation of the compound fruit, and notice that each part is
like a little plum or cherry.
3. =The cherry.=—Similarly examine cherry blossom (Fig. 77). The
pistil consists of one carpel, and is fixed at the bottom of the
receptacle-cup, while the calyx, corolla, and stamens are fixed on the
margin of the cup. Trace the origin of each part of the fruit.
Compare the plum and apricot.
[Illustration: FIG. 74.—Apple Blossom. (× ⅓.)]
[Illustration: FIG. 75.—Wild Rose. (× ⅓.)]
4. =The apple and pear.=—Cut vertically through an apple blossom (Fig.
74) or pear blossom (Fig. 78), and notice that the ovary is embedded in
the receptacle, and that calyx, corolla, and stamens are fixed on the
top of this. Cut across the ovary and see the five divisions (carpels).
The eatable part of the fruit is the swollen receptacle. Compare the
hawthorn.
=The wild rose.=—The plants of the rose family are, most commonly,
woody trees or shrubs. The leaves are provided with stipules in nearly
all cases. The =wild rose= (Fig. 75) may be taken as a type of the
group. It bears a superficial resemblance to a buttercup, but on
dissection considerable difference in the arrangement of the parts is
seen. In the rose, the receptacle is urn-shaped; from the margin of the
urn spring the five sepals, five petals, and numerous stamens; while
inside the urn the separate carpels of the pistil are inserted. In the
=blackberry= (Fig. 76), =raspberry=, and =strawberry= the receptacle is
knob-shaped, and the carpels are arranged on the outside of the knob,
somewhat as in the buttercup. Here again, however, the calyx, corolla,
and stamens differ from those of the buttercup in seeming to arise from
a common base.
[Illustration: FIG. 76.—Blackberry. 1, flowering branch (× ⅓); 2,
longitudinal section of flower (× 1); 3, fruit (× ⅓); 4, diagram of
flower.]
[Illustration: FIG. 77.—Cherry. 1, flowering branch (× ⅔); 2,
longitudinal section of flower; 3, longitudinal section of fruit.]
The differences between the rose, blackberry, raspberry, and strawberry
are more marked when the pistil has become a fruit. The fleshy part of
the rose hip is the urn-shaped receptacle which encloses the ripened
carpels. In the case of the blackberry and raspberry the receptacle
is dry, and is surrounded by the compound fruit (Fig. 76, 3) of the
several bodies like little plums or cherries. The eatable part of the
strawberry fruit (Fig. 144) is the swollen receptacle, on the outside
of which are the little yellow nutlets derived from the carpels of the
flower.
In the =cherry= (Fig. 77), =plum=, and =apricot= the pistil consists
of only one carpel, which is enclosed in the urn-like receptacle.
After fertilisation, the greater part of the wall of the ovary becomes
fleshy, and one of the two ovules contained in it becomes a seed. The
“stone” is formed from the innermost part of the ovary wall.
The =apple= (Fig. 74) and =pear= (Fig. 78) have their five carpels
embedded in the receptacle, and the rest of the flower stands on this
part. The eatable portion of the fruit is the swollen receptacle. The
=hawthorn= has usually only two carpels, and in the fruit the part
derived from the receptacle becomes hard and horny. In other respects
it is very similar to the apple.
[Illustration: FIG. 78.—Pear. 1, flowering branch (× ⅔); 2,
longitudinal section of flower; 3, longitudinal section of fruit; 4,
diagram of flower.]
The rose family is widely distributed, especially in temperate regions.
20. THE PARSLEY FAMILY.
1. =The poison hemlock.=—Examine this plant (Fig. 79) very carefully,
remembering that it is poisonous. Notice the general habit of growth;
the characters of the sheathing, compound leaves; the hollow ribbed
stem; and also the arrangement of the flowers, which is characteristic
of the family. From the top of a main flower-stalk several smaller
stalks come off together, like the ribs of an umbrella. From the top of
each of these spring the stalklets which bear the small white flowers.
Notice the _bracts_ at the points of origin of the stalks. Examine
the flowers, and watch insects visiting them. Which insects are most
commonly found on the flowers?
Compare the cow parsnip, the water hemlock, carrot, parsley, parsnip,
and celery, carefully noting the points of resemblance and difference.
[Illustration: FIG. 79.—Poison Hemlock. (× ¼.)]
[Illustration: FIG. 80.—Hedge Parsley. (× ⅙.)]
=The parsley family.=—The plants of this family may be recognised
easily by the arrangement of the flowers. Several stalks spring
together from the top of the main flower stalk and each of these again
gives rise at its tip to a number of smaller stalks, at the ends of
which the small flowers are borne (Figs. 79 and 80). The flowers are
fertilised by the aid of insects, and as the nectar is on the surface
it is accessible to small insects such as flies, beetles, etc. The
flowers are rendered more conspicuous by being placed close together.
The stems are usually hollow, and the leaves are alternate, and
generally compound, with sheathing bases. Many of the plants of this
family are very poisonous, and such should be carefully distinguished
and whenever possible exterminated.
The =poison hemlock= (Fig. 79) varies in height from two to seven
feet. It has a hollow stem which is spotted with purple in the lower
part, and when bruised the leaves give off a smell like that of mice.
Cattle are often poisoned by eating the plant in hay, and children
have been poisoned even by blowing whistles made from the stem. The
=water-hemlock= is extremely poisonous. It grows along the sides of
pools. The stem is hollow, and the leaflets of the compound leaves
are finely toothed. The root is a cluster of fleshy swellings, and
has unfortunately a rather pleasant taste. Other poisonous plants of
the family are the =water dropwort= and the =fool’s-parsley=. Among
the harmless and useful members of the group are =celery= (when
cultivated), =carrot=, =parsnip=, and =parsley=.
21. THE PRIMROSE AND COWSLIP.
1. =The primrose.=—Examine the habit (Fig. 81) of the plant, its
underground stem, its spoon-shaped leaves—arranged in a rosette—and
the manner in which the flowers spring from the stem. In the flower
make out (_a_) the _calyx_, 5-pointed and with united sepals; (_b_)
the _corolla_, consisting of 5 petals united below into a tube. Tear
down the corolla-tube to see (_c_) the 5 _stamens_ inserted on the
corolla-tube. In some (“thrum-eyed”) flowers the anthers are at the top
of the tube; in others (“pin-eyed”), they are halfway down; (_d_) the
_pistil_, consisting of stigma, style, and ovary. In thrum-eyed flowers
the style is short and the stigma is halfway down the corolla-tube;
while in pin-eyed flowers the style is long and the stigma is at the
top of the tube. Do you find both pin-eyed and thrum-eyed flowers on
the same plant, or does one plant bear only one kind?
2. =Fertilisation.=—Cover up a plant of each kind with gauze, to keep
insects from the flowers, and notice whether the covered flowers ripen
seeds like the others.
3. =The cowslip.=—Compare the cowslip (Fig. 83), and notice that the
main stalk gives off from the same point several smaller stalks,
each of which bears a flower. Observe that the cowslip also has both
pin-eyed and thrum-eyed forms of flowers.
[Illustration: FIG. 81.—Primrose. (× ¼.)]
=The primrose and cowslip.=—In the primrose we have flowers of a
type differing from all those previously considered in this chapter.
Not only are the sepals joined together to form a five-toothed
=calyx-tube=, but the five petals are also joined together to form a
=corolla-tube=, and the stamens are fixed on the corolla-tube. There
are two kinds of primroses, known to country children as pin-eyed
and thrum-eyed flowers respectively (Fig. 82). The two forms grow
on separate plants. In a pin-eyed primrose the style is long, and
the stigma—looking somewhat like the head of a pin—is at the top of
the corolla-tube; while the stamens are halfway down. The thrum-eyed
primroses have their stamens at the top, while the stigma of the pistil
is halfway down the tube, exactly opposite the place where, in the
pin-eyed form, the stamens are inserted. This curious state of things
was a great puzzle to botanists until Darwin cleared up the mystery. A
bee, thrusting its proboscis down a pin-eyed primrose in search of the
nectar at the bottom, dusts it with pollen about halfway down—just in
the place which will come in contact with the stigma when the animal
visits a thrum-eyed flower. And the pollen from the thrum-eyed form
adheres to the part of the bee which will presently touch the stigma of
a long-styled flower. This beautiful and simple arrangement makes it
practically certain that each primrose shall be fertilised by pollen
from the other form. In the thrum-eyed form, however, it is possible
for pollen to fall upon the stigma and produce self-fertilisation.
[Illustration: FIG. 82.—Chinese Primrose. _L_, long-styled (“pin-eyed”)
flower; _K_, short-styled (“thrum-eyed”) flower; _G_, stigma; _S_,
anthers.]
[Illustration: FIG. 83.—Cowslip. (× ⅙.)]
It is obvious that the cowslip (Fig. 83) is closely related to
the primrose. The difference lies chiefly in the character of the
flower-stalk. In the cowslip this is long, and it bears at its top
several stalklets, each of which ends in a flower. As in the primrose,
cross-fertilisation is secured by some flowers being pin-eyed (long
styled) and others thrum-eyed (short styled).
22. THE DAISY AND ITS RELATIVES.
1. =The daisy.=—Take up several daisy plants (Fig. 84) entire, and
wash away the soil from the roots. Notice how the stems—some of which
are underground—are connected together. Draw a leaf. What advantage is
it to the plant to have leaves of the shape noticed? Cut vertically
through the “head,” and notice that what is usually called the “flower”
really consists of a large number of small flowers.
[Illustration: FIG. 84.—Daisy. (× ¼.)]
The central or _disc flowers_ are tubular. Which disc flowers
open first, those near the middle or those nearer the edge of the
disc? Pick off a flower and notice the 5-toothed corolla. Tear the
corolla down with a needle, and observe the tiny stamens (5) fixed
on the corolla-tube. The anthers are joined together. Notice the
divided stigma of the pistil. The white and pink _ray flowers_ have
strap-shaped corollas. They have no stamens, but each has a pistil
like that of a disc flower. What do you think is the object of the ray
flowers being so conspicuous? Why do they close over the disc at night?
Notice the large number of green _bracts_ below the disc.
2. =The dandelion.=—Compare the dandelion (Fig. 85). Notice that all
the flowers are strap-shaped, like the ray flowers of the daisy. Pull
one out, and make out the strap-like corolla, the five stamens with
joined anthers, and the double stigma (Fig. 86, 2). Notice the tuft of
fine hairs below the corolla and above the knob-like ovary. The tuft of
hairs is the top of the calyx-tube.
When the flowers have been fertilised, the yellow corollas wither, and
each calyx-tube elongates until it is about an inch long, the tuft
of fine hairs being still at the top (4). Blow a “clock,” and notice
how easily the fruits are detached from the disc and how slowly they
settle. What advantage is this to the plant?
[Illustration: FIG. 85.—Dandelion. (× ¼.)]
3. =The thistle.=—Compare the thistle (Fig. 87). The bracts are very
prickly. Is this an advantage? Are the flowers tubular or strap-shaped?
Examine the fruits (“thistle down”) and compare with those of dandelion.
=The daisy.=—What is generally called the “flower” of the daisy (Fig.
84) really consists of a very large number of small separate flowers
set close together on a flattened disc or receptacle. The group of
flowers is called a =head=. On the lower surface of the head are
several green leaves, or bracts, which protect the bud before it opens.
The flowers of a daisy-head are of two kinds. The white or pink straps
set round the edge of the head are the corollas of the ray flowers.
They have no stamens, but a pistil with a divided stigma is present in
each. The disc flowers are yellow and tubular. The corolla consists of
five united petals. On it are fixed five stamens, the anthers of which
are joined together. The pistil is like that of a ray flower. No calyx
is present in either the ray or disc flowers of the daisy.
The daisy is fertilised by the aid of insects which are attracted by
the strap-like corollas of the ray flowers.
[Illustration: FIG. 86.—Dandelion. 1, two heads and a leaf (× ⅔); 2, a
single flower (× 2); 3, fruit (× ⁸/₃); 4, receptacle, with one fruit.]
The =dandelion= “flower” (Fig. 85) is also really a head consisting of
a great many separate flowers. There are often between two and three
hundred of these little flowers present in one head. Below the head
are several green bracts, and these protect the flowers both in the
bud and at night (Fig. 86). The flowers of the dandelion are all of
one type. The corolla is strap-shaped (Fig. 86, 2), and of a beautiful
yellow colour to attract insects. On the end of the strap may be seen
five small teeth which indicate that it really consists of five united
petals. At the base of the corolla is a tuft of fine hairs, which is
the top of the calyx-tube, and at the bottom of the flower is a little
white knob—the ovary. The five stamens are fixed on the inside of the
corolla tube. Their anthers are united to form a tube through which the
upper part of the style, and the forked stigma protrude.
[Illustration: FIG. 87.—Thistle. (× ¼.)]
[Illustration: FIG. 88.—Tubular flower of Thistle (magnified).]
It will be noticed that a dandelion flower is practically like a ray
flower of a daisy, with the addition of calyx and stamens.
The =thistle= (Fig. 87) is another common member of the family. Its
bracts are prickly, and are a protection from the attacks of animals.
The flowers (Fig. 88) are all tubular. The common thistle distributes
its fruit by a plume of radiating fine hairs—the calyx. The fruit is
commonly known as “thistle down.”
The =Compositae=, as plants of this family are called, are found in all
parts of the world. The family is the largest in the vegetable kingdom,
and many of the plants included in it are of considerable importance.
23. THE FOXGLOVE FAMILY.
1. =The foxglove.=—Examine a flowering plant of foxglove (Fig. 89).
Notice the general habit of growth. In the flower make out the
five-lobed calyx, the irregular corolla with five petals joined to form
a tube, the four stamens (two long and two short) fixed on the corolla
tube (Fig. 90), and the form and attachment of the pistil. Watch bees
visiting the flower. 2. =The speedwell.=—Compare the speedwell (Fig.
91), and notice that the corolla is more nearly regular than is the
case with the foxglove, that it consists of _four_ combined petals, and
that _two_ stamens are fixed upon it.
3. =The musk.=—Compare the musk. Dissect a flower and notice the forms
and positions of the parts. Especially examine the pistil with its
two-lobed stigma. With a hair, carefully touch one of the lobes of the
stigma of a growing flower and watch how the lobes close. Do the lobes
open again? Put a little pollen on, and watch to see if this time the
lobes open again after closing.
Watch insects visiting the flowers and try to make out how the
pollination of the stigmas is brought about.
=The foxglove family.=—In the primrose and the disc-flowers of the
daisy are seen examples of regular, dicotyledonous flowers with five
petals fused to form a corolla-tube, and with five stamens inserted on
the corolla. In the strap-shaped flowers of the dandelion the corolla
is irregular, but still consists of five fused petals and bears the
five stamens.
[Illustration: FIG. 89.—Foxglove, (× ⅙.)]
The =foxglove= (Fig. 89) and its relatives have also irregular corollas
of joined petals on which the stamens are fixed; but the stamens
are usually only four in number, two being long and two short as
in Fig. 90, _b_. In the foxglove the stamens ripen and shed their
pollen before the pistil of the same flower is mature. This prevents
self-fertilisation, but bumble bees in passing from one flower to
another convey the ripe pollen of the younger flowers to the stigmas of
flowers which are ready for fertilisation.
[Illustration: FIG. 90.—Foxglove. _a_, flower; _b_, corolla cut open
and spread out; _c_, calyx and pistil; _d_, fruit; _e_, section of
fruit. (× ⅔.)]
The pretty blue =speedwell= (Fig. 91) is closely related to the
foxglove, but its corolla has only four lobes instead of five, and some
times these seem of almost equal size at the first glance. Generally,
however, the corolla is very plainly irregular. The speedwell has only
two stamens, while =mullein= has five.
[Illustration: FIG. 91.—Speedwell. (× ½.)]
=Calceolaria=, =musk=, =gloxinia=, and =snapdragon=—other members of
the family—are often cultivated in gardens.
The flowers of the musk are especially interesting, because they
show so well what is called =irritability=,—the power which all
living things possess of acting in a definite manner in response to a
definite irritation or stimulus. We have already seen good examples
of plant-irritability in the way a climbing stem winds itself round
a support. The stigma of the musk flower has two flaps. If these
are touched with a hair or bristle they quickly close together, but
presently open again as if they had found out that they had been
tricked. When, however, a little pollen is put on the flaps they close
finally, for their whole object is accomplished.
Some of the plants in this family are poisonous, the foxglove being
especially so in all its parts.
24. THE LABIATES.
1. =The deadnettle.=—Examine a deadnettle plant (Fig. 92). Notice
the habit of growth, and write down a description of the shape and
appearance of the stem and leaves. What is the shape of the flower? How
many sepals, petals, and stamens has it? Do the stamens ripen first, or
does the pistil? What insects do you find visiting the flower? Try to
find out how they pollinate the stigma.
[Illustration: FIG. 92.—White Deadnettle. (× ⅙.)]
2. =Other labiates.=—Compare the sage (especially in respect of its
relation to bees), rosemary, thyme, marjoram, and mint, and distinguish
between their various flowers, leaves, and scents.
=The labiates.=—The deadnettle is a type of an easily recognisable
family of plants. The stem is square in section, and the leaves are
arranged upon it in opposite pairs at right angles to each other. The
plants are hairy and have distinctive odours. The aroma of =thyme=,
=mint=, =marjoram=, =sage=, etc., has led to the plants being used for
flavouring food. None of the labiates is poisonous.
The shape of the flower is very characteristic, and is specially
adapted to the visits of bees. The flowers are so modified that the
lowest part of the corolla forms a platform on which the bee may
conveniently alight, while the upper petals unite into an arched roof
which protects the pistil and stamens.
[Illustration: FIG. 93.—Pollination of the Sage by a bumble bee. For
explanation see text. (× 1.)]
The mechanism of cross-pollination is particularly well shown in the
case of the =sage= (Fig. 93). The flower contains four stamens, but two
of these have lost their use, and the others are modified in a strange
manner. The whole stamen has somewhat the shape of a capital T, and at
each end of the cross-piece is a pollen box. Usually the cross-piece
(_c_, Fig. 93, 3) is not at right angles to the filament, but is swung
up—the junction acts as a hinge—until it is nearly vertical (Fig. 93,
4). The pollen box _s_, which is at the lower end of the cross-piece
_c_ when this is vertical, contains hardly any pollen. The entrance to
the honey tube is thus guarded by two pillars, the filaments (_f_) of
the stamens; and the lower pollen box (_s_) of the cross-piece of each
stamen is directly in front of the bee’s head as it stands on the lower
lip of the flower. When it pushes forward its head to reach the nectar
it comes in contact with the lower pollen boxes, and the cross pieces
swing round on their hinges, bringing the upper pollen boxes down with
a smack on the bee’s back (Fig. 93, 1), and sprinkling it liberally
with pollen dust. Having shed their pollen the stamens shrivel up, and
the pistil comes to maturity. As the pistil ripens, the stigma arches
over (Fig. 93, 2) so as to scrape along the back of any bee visiting
the flower for the nectar, and thus to wipe off the pollen which has
been brought from a younger flower.
25. THE LILY AND SNOWDROP FAMILIES.
1. =The hyacinth.=—Take up a plant (Fig. 94) entire and notice the
underground bulb with roots springing from its lower surface, and the
long narrow leaves. Is the venation of the leaves parallel or net-like?
Is the hyacinth a monocotyledon or a dicotyledon? See the bract at the
base of each flower-stalklet.
Examine the flower. Its leaves cannot be distinguished into calyx
and corolla, but are quite similar to each other in size, shape, and
colour. They are therefore called the _perianth_. The perianth leaves
are united to form a tube. Tear down the tube to see the six stamens
fixed on it. Are they all on the same level? Examine the pistil and cut
the ovary across to see the ovules in the three joined carpels. Which
is fixed at the higher level, the perianth or the base of the pistil?
2. =Other plants of the lily family.=—Examine also the white lily,
tulip, star of Bethlehem, and lily of the valley, and notice that in
spite of small differences they are all monocotyledons (how do you know
this?) and all have the _perianth fixed below the ovary_.
3. =The snowdrop.=—Compare and contrast the snowdrop (Fig. 95). Make
out that it is a monocotyledon, but that its _perianth is inserted
above the ovary_. This is the great point of difference from the lily
family. Notice also how the stamens are fixed.
[Illustration: FIG. 94.—Wild Hyacinth. (× ¹/₁₀.)]
[Illustration: FIG. 95.—Snowdrops. (× ¼.)]
4. =Other plants of the snowdrop family.=—Examine the daffodil (Figs.
55 and 96) and narcissus. Arising from the short perianth tube of the
daffodil is a longer one which is often mistaken for a corolla; it is
called the _corona_. None of the flowers hitherto described contains
anything corresponding to a corona. The corona in the narcissus is
short. As in the snowdrop, the perianth is fixed _above_ the ovary.
Observe how the stamens are fixed, and notice the dry leaf beneath the
flower.
=The lily family.=—Either the =wild hyacinth= (Fig. 94) or the
cultivated single hyacinth may be taken as a good representative of
this family. The first point which strikes the student on examining the
general “habit” of the plant is the character of the long sheathing
leaves. Their veins do not form an obvious network, such as is seen in
the leaves of dicotyledons, but run lengthwise and roughly parallel
to each other in the manner characteristic of grasses and other
monocotyledons (p. 40). The leaves are narrow, and are not divided into
blade and stalk; they and the flower stalk spring from an underground
bulb (p. 84) which consists chiefly of the swollen leaf-bases of
a previous season. A separate calyx and corolla are not to be
distinguished in the flower; the six leaves being all alike in size,
shape, and colour. These six leaves hence receive a special name, and
are called the =perianth=. The perianth leaves are united into a tube,
on the inside of which the six stamens are arranged in two series of
three each. In the middle of the flower, and fixed _above the insertion
of the perianth_, is the pistil, which consists of three united carpels.
[Illustration: FIG. 96.—Daffodil flower, cut down the middle. (× ⅔.)]
It will be noticed that the parts of the flower are in threes. There
are six united perianth leaves (three inner and three outer), six
stamens (also in two series), and three united carpels. This is very
common—though by no means universal—in monocotyledons.
All the plants of the lily family—including the tulips, the true
lilies, lily of the valley, asparagus, onion, etc.—agree in being
monocotyledons, and in their flowers having a conspicuous perianth (for
attracting insects) and six stamens, and in the ovary being above the
insertion of the perianth.
=The snowdrop family.=—Plants of this family are very similar to those
of the lily family; in fact in only one respect can any sharp line of
demarcation be drawn between the two groups; in the snowdrop and its
relatives the other parts of the flower stand _upon the ovary_ (Fig.
96). The flowers of some plants of the family, _e.g._ the daffodil,
possess a tubular outgrowth of the perianth, which is called a
=corona=. It is often mistaken for a corolla.
26. THE ARUM LILY.
1. =The cuckoo-pint.=—Examine the habit of the plant, and then cut open
the “flower.” You will probably find a number of small flies inside.
Examine the central rod and make out the stamens and pistils on it.
Which ripen first?
=The arum= “=lily=,” with its humble relative the cuckoo-pint (Fig.
97), merits special mention; for, in the first place, it is not a lily
at all, and secondly, it furnishes an extremely interesting example of
pistils coming to maturity before anthers, which is rather rare.
What is generally called the “flower” of the cuckoo-pint, or “lords and
ladies,” consists of a big curled leaf with a purple rod sticking up in
the middle. Near the bottom of the rod, but hidden from sight by the
lower part of the leaf, the true flowers arise. The chamber containing
them is shut in by a series of stiffish hairs which point downwards.
Below the hairs the rod supports a series of anthers and, near the
bottom of the chamber, several pistils. On cutting open the chamber
one nearly always finds a number of small flies, covered with pollen,
which they have brought from another arum. The flies get in easily
enough, but once in they are prisoners, for the down-pointing hairs
prevent them from getting out again. The pistils near the bottom of the
rod ripen, and are fertilised by the pollen the flies have brought.
After a time the anthers above ripen and shed their welcome pollen
on the hungry captives. Soon after this the hairs at the top of the
chamber shrivel up, and the flies, once more covered with pollen, are
at liberty to return to the outer world and, untaught by experience, to
repeat the experiment on another “flower.”
[Illustration: FIG. 97.—_A_, Cuckoo-pint. (× ¼.) In _B_, the front of
the leaf is cut away to show the rod _sp_ (_C_). _F_, female flowers;
_M_, male flowers; _st_, undeveloped male flowers.]
EXERCISES ON CHAPTER VI.
1. Describe the arrangement of the stamens in the
wallflower, the sage, and the primrose.
2. Describe the pistil of the deadnettle, the primrose, and
the shepherd’s purse. (1895)
3. In what respects does the flower of the buttercup differ
from that of the wild rose?
4. Explain the arrangement and form of the stamens in some
flower selected by yourself. Describe the structure and
contents of the anther. (1897)
5. Where is the pollen of a flower formed? What is its use? (1898)
6. Name one or two plants which do not ripen seed if insects
are excluded, and show why they do not. (1898)
7. Name two plants which would be in flower in each of the
months from March to August inclusive, and state in what
localities they would be found? (N.F.U.)
8. In what ways are insects attracted to visit flowers? Give
examples, with an explanation and drawing in each case, of
any special structure which may be a means of attraction. (N.F.U.)
9. Name ten flowering plants which may be found, (_a_) in a
shady wood, (_b_) in a meadow, in late spring.
10. Name any fresh specimens of flowers which usually could
be obtained growing wild in March, June, and October
respectively. (N.F.U.)
11. What wild flowers would you expect to find in early
April in your part of the country? In what kinds of places
would you look for them? (N.F.U.)
12. Name the parts of any flower you have examined which
are concerned with the production of seed.
(King’s Scholarship, 1904)