30. THE OAK FAMILY.
1. =The oak.=—(_a_) _Habits of growth._—Examine an oak tree growing
in an exposed situation. What is its approximate height? Estimate the
diameter of the trunk at (_a_) the ground level, (_b_) at heights of 1,
2, 3, 4, etc., feet. At what height do the principal boughs come off?
About what angle do the boughs make with the trunk? Are they straight,
evenly curved, or zig-zag? Contrast in these respects an oak growing in
a plantation. Try to account for the differences observed.
(_b_) _The bark._—Examine the barks in oaks of various ages. Do the
ridges and furrows caused by the splitting of the bark form any
definite pattern, or are they arranged anyhow? Find a piece which shows
the pattern well, and make a drawing of it.
(_c_) _Method of branching._—Carefully observe the tree from a
distance, and notice how the great boughs spring from the trunk, and
in their turn give rise to smaller and smaller branches. Notice the
shape of a tuft of the smallest twigs against the sky; then close your
eyes and try to recall the picture. A still better way is to make a
careful drawing of the tree, not attempting to put in details, but
paying special attention to the trunk and main branches, and to the
general massing of the twigs. What is the general “expression” of the
tree? Would you call it, _e.g._, graceful, formal, sturdy, delicate,
stiff, or sombre? The method of branching is best seen in the winter or
spring, when the tree is leafless.
Examine a twig in winter or spring, and notice the position of the
buds. Round the tip there may be three or more crowded buds. The one
at the tip generally dies, and those just behind grow out into lateral
branches. Can you see any trace of this having been the case with the
big boughs? On a twig make out—from the marks on the outside—the growth
of last year, two, three, and four years ago. Cut these lengths across
with a sharp knife, and count the rings of wood.
(_d_) _The leaves._—Watch a marked twig from spring to summer, and
notice how short are the new shoots which come from the buds, and
consequently how close together the new leaves are. Does this account
for the crown of foliage on the tree being so dense? Make a drawing of
an oak leaf. At what time of the year do (i) the leaf-buds open, (ii)
the leaves fall from the tree? In winter, try to find an oak which has
not shed its leaves; is it a young tree or an old one?
(_e_) _The flowers._—In May notice (i) the hanging catkins, each of
which is a bunch of _male flowers_ containing stamens, but no pistil;
(ii) the groups of small _female flowers_ which arise in the axils of
two or three of the upper foliage leaves; each contains a pistil, but
no stamens. Notice the cup of scaly bracts, which surrounds the lower
part of a female flower. Does the tree flower before or after the leaf
buds have expanded?
(_f_) _The fruit._—Trace the development of the acorn from the female
flower, and the change of the covering of scales into the woody cup. If
possible, compare for some years the yield of acorns by a selected old
oak. Germinate an acorn.
(_g_) _Associated animals._—Make as full a list as possible of the
animals which you have seen obtaining food or shelter from the oak.
What was each doing when you saw it? Look for _galls_—the so-called
“oak apples”—and cut them open to see the insect inside. Also examine
the other kinds of galls found on the leaves and catkins.
[Make similar observations, sketches, and notes of other forest-trees,
in addition to the special observations mentioned below, and learn to
recognise their “expressions,” methods of branching, bark, leaves,
flowers, and fruit.]
2. =The beech.=—Notice the smooth, olive-grey bark, and the “fluted
column” appearance of the base of the trunk of many beeches; the long,
wavy boughs; the brown, sharp leaf-buds; the smooth, silky-fringed
leaves; the scarcity, or absence, of vegetation beneath the tree; the
hanging, globular catkins of male flowers; the pairs of female flowers,
surrounded by prickly scales. Make notes of the dates of flowering and
opening of the leaf-buds. Trees may be considered in flower when the
stamens can be seen. Trace the development of the fruit or “mast.” Each
pair of flowers gives rise to two three-sided nuts, enclosed in a woody
cup or husk. It is covered with hard bristles, and splits into four
parts when ripe.
Compare the _sweet chestnut_.
3. =The birch.=—Observe the graceful appearance of the tree; the
slender trunk, with its bark streaked with brown, yellow, and silver;
the purple-brown colour and wiriness of the young twigs; the shape
and size of the dark green leaves, and the cylindrical, many-flowered
catkins. The male catkins appear in the autumn, the smaller female
catkins in the following spring. Examine the two kinds of flowers. Find
an old birch-cone and break it open to see the winged fruits. What is
the use of the wings?
4. =The hazel and alder.=—In what situations do these trees grow?
Compare them with the birch. Notice that in both hazel and alder the
male flowers are in long, dangling catkins. The groups of female
flowers of the hazel look almost like leaf-buds, but can be recognised
by the spreading red stigmas. The female flowers of the alder form
distinct cones. Is the flowering part of the twig of this year’s or
last year’s growth? Look in the autumn for the cones and catkins which
will expand next spring. Trace the development of the fruit.
=The oak.=—The student cannot better commence the study of forest
trees than by selecting one as a type, and making himself thoroughly
familiar with its life-history, and with its appearance at all times
of the year. Other trees should then be compared and contrasted point
by point, is and with each other. The oak answers admirably as such a
central type. It is perhaps the best-known of all British forest trees,
not only from its wide distribution, but also from its historical and
legendary associations.
[Illustration: FIG. 112.—The Oak.]
The oak (Fig. 112) flourishes in exposed and sunny situations,
especially where the soil is well drained. It can be recognised by
the zig-zag and wide-spreading boughs, which often spring from the
trunk almost horizontally. A very strong form of trunk is plainly
necessary to support such branches, and in an old solitary oak it may
often be seen that the bole is very thick at the ground line, and then
rapidly narrows, until at a height about equal to the base-diameter it
may be only half or one-third the thickness. Above this point it is
practically cylindrical up to the origin of the boughs, where it is
swollen. An oak growing in a wood, or plantation, is of very different
form. Its trunk is tall and straight, and the larger boughs are not
given off until near the top. To secure the necessary light, the tree
used its energy in growing in length, and in keeping pace with its
neighbours rather than in spreading laterally. In such a crowded oak
the lateral buds generally remain undeveloped, while the end of the
shoot pushes onwards and upwards to the light. The opposite is the case
when there is plenty of room and light on all sides. Then it is usually
the terminal bud which dies, while the lateral buds grow out into
branches, forming the “knee-joints” which were once so greatly valued
for shipbuilding.
The bark of the oak is very rugged, with ridges and furrows running
almost vertically.
[Illustration: FIG. 113.—The Oak; leaves, flowers and fruit. _A_,
flowering branch (× ¼); _B_, a male flower (magnified); _C_, stamens
(magnified); _D_, a female flower (magnified); _E_, acorns; _F_, cup of
acorn; _G_, _H_, seed.]
The young shoots which are formed when the buds expand in spring are
short, and the leaves are set closely together. As a result, the oak’s
foliage is characteristically dense and thick. The leaves are very
distinctive; their general shape is oval, and the margin is deeply and
irregularly lobed (Fig. 113).
If in early spring we go out in the woods and fix on an old oak tree
(the oak hardly ever flowers before it is 50 years old), we shall
probably see the =flowers= on some of the young twigs. The _female
flowers_—one to five on each flower-stalk—are near the end of the
twig, while the male flowers arise lower down. The female flowers are
destitute of stamens, each consisting practically of a single pistil,
partially enclosed in two envelopes, the lower of which ultimately
becomes the familiar “cup” of the acorn. The stigma has three
spreading lobes for receiving pollen. The _male stalks_ or catkins,
hang down from the lower part of the twig, and every stalk bears about
a dozen flowers. The male flowers have each from 5 to 12 stamens, but
they have no pistil. The stamens produce pollen in the usual way, and
when they burst, the wind blows the loose pollen from the stamens and
scatters it in the air. Some of the pollen dust is almost certain to be
wafted to the stigmas of the female flowers, and the pollen grains put
out tubes, and in due course fertilise the ovules.
[Illustration: FIG. 114.—The Beech.]
Most of our forest trees resemble the oak in being pollinated by the
aid of the wind. It is evident that for the process to be successful
the trees must flower early in the spring, before the foliage has
become so thick as to be in the way of the pollen and prevent it from
reaching the stigmas of the female flowers. It is also important that
the pollen may be easily detached, and it is for this purpose that the
male flowers of the oak and similar trees hang down in the familiar
=catkin= fashion.
[Illustration: FIG. 115.—The Beech. 1, flowering branch (× ⅔); 2, a
male flower (× 4); 3, a female flower cut through longitudinally (× 2);
4, cross section of ovary; 5, cup and fruits (× ⅔); 6, fruit.]
After fertilisation the female flower changes into an =acorn= (Fig.
113, _E_), a nut enclosed in a cup. The nut contains a single large
seed, which on germination grows up into a new oak.
=Galls= of various kinds are to be found on most oaks. These are
excrescences caused by certain insects having laid their eggs in the
soft tissues beneath the surface. More than fifty species of insects
obtain their food from the oak. Some of these will be referred to in a
later chapter.
[Illustration: FIG. 116.—The Birch.]
=The beech.=—The beech (Fig. 114) is easily recognised by the
olive-grey, smooth bark, and by the shape of the base of the trunk,
which usually has the appearance of being formed by the union of
several separate columns. When well grown the tree is lofty, and bears
a wide-spreading crown of branches which, when clothed with leaves in
summer, casts a dense shade. The ground beneath the tree is generally
destitute of other vegetation. The winter-buds are long and pointed;
they expand in May, the new shoots at first drooping, but straightening
out in a fortnight or so. The leaves (Fig. 115) are broad, thin, and
glossy, and are fringed with fine, silky hairs. Young beeches, like
young oaks, often retain their leaves through the winter.
The tree is in flower by the time the foliage has fully developed. The
male flowers are borne in small, rounded catkins (_a_, Fig. 115). The
female flowers (3, Fig. 115) are in pairs. Each pair is surrounded by
prickly scales, and gives rise after fertilisation to two three-sided
and pointed nuts enclosed in a woody cup or husk. The husk is covered
with hard, blunt prickles, and when ripe splits into four parts.
Beeches do not harbour many insects, but squirrels frequent them for
the sake of the nuts. The prickly husks protect the fruit from being
eaten before it is ripe.
[Illustration: FIG. 117.—The Birch; leaves, flowers and fruit. 1,
branch with male (_b_) and female (_a_) catkins (× ⅔); 2, bract with
three male flowers (× 2); 3, bract with three female flowers (× 4); 4,
ripe cone (× ⅔); 5, fruit (× ⁴/₃).]
The =Spanish=, or =sweet chestnut= is allied to the oak and beech. It
has long, narrow leaves; it flowers in July. Its fruit is enclosed in a
prickly husk, which splits into four when the nuts are ripe in October.
=The birch.=—The birch (Fig. 116) is a slender, graceful tree, with
bark streaked with brown, yellow, and silvery patches. Its leaves (Fig.
117) are rather small, and their glossy, dark-green colour contrasts
pleasantly with the brownish-purple of the young twigs. Both male and
female flowers are arranged in catkins (Fig. 117). The male flowers
appear in autumn, but do not open until spring, when the newly-formed
female flowers are ready. The female catkins (_a_, Fig. 117) are much
smaller than the male (_b_).
[Illustration: FIG. 118.—The Hazel; leaf, flowers and fruit. 1, a
flowering branch (× ⅔); 2, a male flower (× 2); 3, a stamen (× 4); 4, a
female flower cut through longitudinally; 5, fruit with cup (× ⅔); 6,
fruit without cup; a foliage leaf.]
[Illustration: FIG. 119.—The Alder; leaf, flowers and fruit. 1, Branch
with male catkins (_a_) and female cones (_b_) (× ⅔); 2, male flowers
(× 2⅔); 3, female cone; 4, two female flowers; 5, ripe cone (× ⅔); 6, a
fruit (× 1).]
The =hazel= and =alder= develop their flowers in the year preceding
their opening. The female flowers of the hazel (Fig. 118) look somewhat
like buds, but may be distinguished by the red stigmas. The fruit is
a nut, enclosed by a sheath of soft bracts. The seeds are largely
dispersed by squirrels. The alder grows on the banks of streams; its
female flowers (Fig 119, _b_) are arranged in short catkins, which may
be called cones. The ripe cone (5, Fig. 119) contains two nuts at the
base of each scale. The fruits fall into the stream, and float away,
perhaps to germinate at a considerable distance.
31. THE WILLOW AND THE POPLAR.
1. =The willow.=—About the third week in March, examine willow trees,
and notice the soft, round, silky bodies which spring alternately
on the young twigs. On some trees these are broad and yellow; they
are _male catkins_ (Fig. 120). Pick off a flower and see the stamens
(generally two stamens to each flower) inserted on a small silky bract
(Fig. 121, _B_). With a lens look for the honey cup at the bottom of
the bract.
On other trees notice the long, narrow, silvery _female catkins_. Pick
off a flower to see the single pistil with the forked style, also on
a small, honeyed bract. Have you ever seen bees visiting the flowers?
Are the catkins as conspicuous when the trees are in leaf? Is it an
advantage to the trees to flower before the leaves come out? In June,
examine the ripened female catkins. Pull out a tuft of the hairy seeds
and dry it in the sun, noticing how they form a fluffy mass. Blow the
mass of seeds. How do you think the seeds are dispersed?
2. =The poplar.=—Find male and female poplars and examine their
flowers. Are the female flowers pollinated by insects or by the wind?
Is self-fertilisation ever possible with willows and poplars? Why not?
Which appear first, the flowers, or the leaves of poplars? Why?
Examine the leaves of the English poplar. Why do they turn over so
easily, even with a very slight breeze? Are both sides of the leaf of
the same colour?
Compare the _Lombardy poplar_ with the English poplar.
=The willow.=—Many species of willow are known, but the sallow
willow—called the =saugh tree= in Scotland—is common in coppices and
hedges. It has purplish brown branches, and large, broad, downy leaves.
In the willow the male and female flowers are produced on different
trees, so that self-fertilisation is obviously impossible. The flowers
of the male willow form broad yellow catkins which cling closely to
the twig (Fig. 121). They are often called “golden palms.” Each flower
consists of two stamens, borne on a silky scale which has a tiny honey
cup at the base. The female flowers form long, narrow, and silvery
catkins; each flower is merely a single pistil with a forked stigma,
and, like a male flower, is supported on a small honeyed bract. The
flowers appear in March, before the leaves, and the catkins are very
conspicuous. They are visited by bees for the sake of the honey and
pollen, pollination being thus effected. In June, the female catkins
are ripe. Each ovary has now become a fruit, which opens and liberates
the silky seeds. When the seeds dry, their fine hairs cling together
so that a light fluffy mass is formed, which can be blown to great
distances by the wind.
[Illustration: FIG. 120.—Twig of male Willow, with catkins. (× ⅙)]
[Illustration: FIG. 121.—The Willow. _A_, flowering male-shoot (× ⅔);
_B_, male flower with bract (magnified); _C_, female cone; _D_, _E_,
female flowers (magnified); _F_, fruit (× ⅔); _G_, the same magnified;
_H_, seed (magnified).]
=The poplar.=—The various poplars are also _completely unisexual_, that
is, any one tree bears either male or female flowers, but not both. In
this case also the flowers appear before the leaves; but the flowers
are pollinated by the aid of the wind, not by insects, and nectaries
are therefore not formed. The catkins are not very much like those of
the willows in appearance, but the fruit and seeds are very similar.
Both willows and poplars are fond of the banks of streams. The English
poplars are graceful trees which can be recognised at a distance by the
manner in which the broad leaves turn on their long stalks, exposing
the lighter-coloured under-surface at the slightest breath of wind.
This is especially noticeable with the =aspen= or trembling poplar
(Fig. 122). The =Lombardy poplar= is a tall, stiff tree.
[Illustration: FIG. 122.—The Poplar. 1, male catkin (× ⅔); 2, female
catkin (× ⅔); 3, male flower (× 2); 4, female flower (× 4); 5, the same
in longitudinal section; 6, fruit; 7, the same after opening; 8, seeds
(× 3); 9, diagram of male flower.]
32. THE ELM, LIME, AND ASH.
1. =The elm.=—Notice the straight trunk, rough bark, and slender
branches of the common elm. Examine the flowers in early spring and
notice that each contains both stamens and pistil. When do the flowers
open? When do the leaves expand? Draw a leaf and a fruit. What is the
use of the broad plate of the fruit?
2. =The lime.=—Observe the straight trunk, smooth bark, and general
_pyramid_ shape of the tree. Draw a leaf, and notice that it is pointed
and is larger on one side of the midrib than on the other. Notice that
the flower stalks spring from leaves (bracts) differing in shape (Fig.
126) and colour from ordinary leaves. Draw one of these leaves with
its attached flower stalk. When do the flowers open? Try to discover
whether bees haunt the flowers. Find out what is the use to the fruit
of the long leafy bract.
3. =The ash.=—Look in winter for the black buds and the flattened
tips of the twigs. When do the flowers open? Notice their rich purple
colour. Examine a flower and make out the two stamens and the pistil.
Trace the formation of the fruit, which is winged and hangs in bunches
called _keys_. What is the use of the wing? When do the leaves expand?
Are they simple or compound? Draw one. What is its colour? When do the
leaves fall?
[Illustration: FIG. 123.—The Elm.]
=The elm.=—The elm (Fig. 123) is usually a lofty tree, easily
recognised at a distance by its straight trunk, slender branches,
and rounded masses of foliage. The bark is rough and very corky. The
tree flowers early in the spring before the leaves are expanded. The
flowers are purple and contain both stamens and pistil. Each fruit
(Fig. 124) is a flat plate with a rounded seed box in the middle; it is
distributed by the wind. The seeds of the common elm do not often ripen
in this country. The leaves (Fig. 124) are rough to the touch, and have
very prominent veins. They do not fall until late autumn.
[Illustration: FIG. 124.—The Elm; leaves, flowers and fruit. 1,
flowering branch (× ⅔); 2, branch with leaves; 3, a flower (× 2); 4,
the same, cut through longitudinally; 5, a fruit (× ⅔).]
=The lime.=—The lime tree (Fig. 125) has a straight smooth trunk.
The tree generally spreads at the base, and tapers to a blunt apex.
The leaves are bright green, heart-shaped, and pointed, and plainly
larger on one side of the midrib than on the other. The yellowish-green
flowers are in bunches, carried on a stalk which springs from
the middle of a long, narrow bract (Fig. 126). The flowers are
complete—calyx, corolla, stamens, and pistil being all present—and are
pollinated by bees, which visit them for the sake of nectar, being
attracted by the sweet scent.
[Illustration: FIG. 125.—Lime Trees.]
[Illustration: FIG. 126.—The Lime. _A_, group of flowers on stalk
(_a_), springing from bract (_b_) (× ⅔); _B_, longitudinal section of
fruit (magnified).]
[Illustration: FIG. 127.—The Ash.]
=The ash= (Fig. 127) is a very graceful tree, and its compound leaves,
with leaflets springing from the sides of the midrib, give the foliage
a characteristically feathery appearance. The bark is ashen-grey in
colour. The tips of the twigs are curiously flattened, and the winter
buds are jet black. The flowers are small, with two purple-black
stamens and a pistil. They open in April before the leaves appear,
forming close clusters. The fruits are long and flat, and hang together
in bunches which are popularly called =keys=. They are only detached
by high winds, and are then blown to considerable distances. The leaves
appear rather late—about the end of May—and are shed early. They
are compound, each consisting of seven or more leaflets arranged in
opposite pairs along the midrib, with a single leaflet at the end.
The =mountain ash= or Rowan tree has leaves somewhat like those of the
ash proper, but in other respects it is quite different, as it belongs
to the rose family (p. 103).
33. THE SYCAMORE AND HORSE CHESTNUT.
1. =The sycamore.=—Observe the size and general shape of the tree.
Examine the twigs in winter and watch the buds open in spring. Draw a
leaf. Why are the leaves usually so sticky in warm weather? Notice the
hanging sprays of green flowers. Are both stamens and pistil present
in the same flower? Are the flowers visited by bees? Why? Follow the
development of the fruit. Draw a pair of fruits. What is the use of the
wing on a fruit? Do the fruits fall off themselves or are they torn
off by gales? Look for seedling sycamores in the woods; also germinate
seeds in garden soil and again observe the various stages.
Compare the _plane_, and notice the pyramidal shape of the tree. The
leaves are very similar in outline to those of the sycamore, but the
flowers are clustered into balls which dangle on long stalks. In
summer, pull off a leaf and observe how the axillary bud is covered by
the cup-shaped base of the leaf-stalk.
2. =The horse chestnut.=—Notice the general shape and method of
branching. These characters, the large buds in winter, and the shape
and size of the leaves in spring and summer, render the tree easily
recognisable at all seasons. Trace the connection between the method
of branching and arrangement of the leaves and buds on the twigs. Note
the date of flowering, and of the unfolding and shedding of the leaves.
Examine the flowers; are they pollinated by insects or by the wind?
Trace the development of the fruit.
[Illustration: FIG. 128.—The Sycamore.]
=The sycamore= (Fig. 128) is one of the best-known trees in this
country, and often grows to a great height. Its leaves (Fig. 33) are
large and five-pointed, the main veins spreading from the top of the
leaf stalk. When young they are of a beautiful red colour. In hot
weather the leaves become very sticky with a sugary syrup called
=honey-dew=. The sycamore is indeed a species of maple, and is closely
related to the sugar maple of North America. In May, the flowers hang
from the twigs in drooping green clusters. They contain both stamens
and pistils, and are visited by bees for the sake of the honey in which
they abound. The fruits or =keys= (Figs. 137 and 4) occur in pairs, or
sometimes three together. Each has a flat, membranous wing, by means of
which it is easily transported by the wind.
In Scotland the sycamore is often called the =plane=. The leaves of the
plane and sycamore are somewhat similar in shape, but the trees belong
to different families. The plane can be identified by its globular
heads of flowers and subsequent balls of seeds, which hang on long
stalks from the twigs.
[Illustration: FIG. 129.—The Horse Chestnut.]
=The horse chestnut.=—The horse chestnut differs from all our other
forest trees of equal size in bearing brilliantly coloured and
conspicuous flowers. The flowers are complete, containing not only
stamens and pistil, but also a calyx and a beautiful pink or white
corolla. The tree has a striking appearance at all seasons of the year.
In winter, the thick twigs, the large terminal buds, and the opposite
lateral buds already described on pp. 62-64 are very conspicuous,
and give an instructive clue to the method of branching. The buds
open early and the new shoots rapidly lengthen, so that the tree is
a mass of foliage whilst most neighbouring trees are still bare. The
leaves (Fig. 26) are compound, consisting of seven large, spoon-shaped
leaflets which spring from a common point at the end of the leaf-stalk.
The flowers open in May. The fruit is ripe in October and then falls to
the ground, its prickly husk splitting into three parts to liberate the
rounded seeds. The leaves fall early, leaving large scars (Fig. 38),
which have some resemblance to the hoof-marks of a horse.
34. CONE-BEARING TREES.
1. =The Scotch pine.=—Notice the shape of the tree: the tall straight
stem and rugged bark, and the dark tufts of foliage. Does the tree bear
leaves all the year round? Does it ever shed its leaves? Are they shed
at any special time of the year? Examine a leafy twig; observe that
the leaves are needle-shaped and come off in pairs. At the apex is a
terminal bud which will continue the length of the twig next season;
the lateral buds below will grow out into twigs at the same time. Try
to make out which parts of the twig grew during last year, and which
during the two previous years.
Notice the cones. The young female cones (_b_, Fig. 130, 1) are erect,
and their scales separate slightly in spring to allow the pollen to
enter. Afterwards they hang down (_c_) whilst the seeds are ripening.
Three years after pollination the scales come apart again to let the
seeds fall out. Examine the seeds from a ripe cone and notice the
attached wings (Fig. 130, 4). Examine cones of various ages. In spring
look for the pointed cones of male flowers (Fig. 130, 1, _a_) which
produce the abundant pollen.
2. =The spruce fir.=—Compare the spruce fir. Notice the conical
_Christmas tree_ shape and the large spreading branches near the
ground. Compare the leaves and cones with those of the pine.
3. =The larch.=—Compare the larch with the pine and spruce. Notice the
drooping boughs, the alternate tufts of leaves, and the small cones
arranged in a row along the twig. Is the larch an evergreen?
=Cone-bearing trees.=—The cone-bearing trees, such as the pines and
firs, are true flowering plants, but of a type which is very different
from any hitherto described. The flowers are peculiar, and form cones,
the male flowers producing pollen and the female flowers ovules. The
ovules, however, are not enclosed in ovaries, but are naked, so that
the pollen gains access to the ovule directly, and is not received on a
stigma. The female cone consists very largely of smooth scales, a pair
of ovules being borne by each scale near its base. The pollen grains
of these trees are rendered particularly buoyant by being blown out at
the sides into little air-filled bladders, and are thus easily carried
by the wind. When the pollen falls on the female cone, the grains slide
down the smooth scales and very likely come in contact with the ovules
at the bottom. Each ovule has a sticky drop of gum at its end, and the
pollen is caught in the gum. Such pollen grains as roll off the upper
scales are almost certain to fall on a lower one and reach the ovules.
=The Scotch pine.=—This is a large tree, with a dome-shaped crown of
foliage. The bark is rough and scaly. Its foliage leaves (Fig. 130) are
long and needle-shaped, and occur in pairs, each pair being carried
by a very short branch. The leaves do not fall off each winter, as do
those of most forest trees, but remain on the branches for three years
or more, so that the younger twigs are clothed with foliage at all
seasons. The cones of male flowers (Fig. 130, 1, _a_) are found at
the base of some of the shoots of the current year. The female cones
(Fig. 130, 1, _b_) are formed round the _ends_ of the young twigs.
They consist mainly of overlapping woody scales, each being knobbed
on its exposed surface and bearing a couple of ovules near the base,
where it springs from the axis of the cone. The young cones are erect,
and in spring (when clouds of pollen are blowing about) their scales
separate slightly to admit the pollen in the chinks between them. After
pollination the scales close again and the cone hangs down (Fig. 130,
1, _c_). The ovules receive the pollen in May, but the actual union, or
fertilisation, does not take place until June of the following year.
The seeds become mature two years after fertilisation. When they are
ripe each bears a thin wing which has split off from the upper surface
of the scale. The scales now separate, and the winged seeds fall out,
to be distributed by the wind. When all the seeds have fallen, the
empty cones drop off the tree.
[Illustration: FIG. 130.—The Scotch Pine. 1, branch with male (_a_) and
female (_b_, _c_) cones; _c_, cone (× ⅔): 2, two views of a stamen (×
2): 3, scales bearing two ovules (× 2): 4, scale with two seeds (_a_),
wing (_b_), seed (_c_): 5, seed in longitudinal section (× 1½).]
Owing to the length of time necessary for the ripening of the seeds,
cones of various ages may be found on the tree all the year round.
=The spruce fir.=—The spruce has a characteristic conical shape, which
is familiar in Christmas trees. The branches are long, and spread
horizontally. The foliage leaves are needle-shaped and four-sided in
section, but are shorter than those of the pine, and are borne singly.
The tree is “evergreen” in the sense that the pine is so, that is, the
leaves are not shed all together, but gradually.
The method of pollination, fertilisation, and distribution of the
winged seeds is similar to that of the pine. In the spruce, however,
the seeds are ripe in October of the year in which the cones are
pollinated.
=The larch.=—The larch is a cone-bearer, and a near relative of the
pines and firs, but it differs from them in shedding its leaves
annually. The leaves are (as is usual in cone-bearing trees)
needle-shaped, but they are very thin and they grow in tufts on short
alternate spurs. The cones are small and are arranged in a row on the
twig. Their scales do not fit so closely together as those of the pine
and fir cones. The larch tree has a conical form, but can readily be
distinguished from the spruce by its _drooping_ boughs, and absence of
leaves in winter.
=Gymnosperms.=—The pines, firs, and larches are neither dicotyledons
nor monocotyledons, but belong to a class of plants which botanists
call =gymnosperms=, in allusion to the fact that their ovules are not
enclosed in ovaries, like those of other flowering plants, but are
_naked_. This is the most ancient and primitive group of flowering
plants known. In fact they form a connecting link between higher
flowering plants and the group to which the ferns and horsetails—which
are still more primitive—belong.
EXERCISES ON CHAPTER VIII.
1. What trees are the first to put on leaves in England?
Which flower before leafing? Which trees are the latest
to come into leaf? When do evergreens, for the most part,
change their leaves? (N.F.U.)
2. Describe the fruit and seed of four of our commonest
trees, explaining in each case how the seeds are
distributed. (N.F.U.)
3. Make observations to find which of the following trees
endure shade most readily—oak, beech, elm, sycamore,
chestnut.
4. What do you suppose are the advantages and disadvantages
of shading and crowding trees, as regards the quality of
the resulting timber?
5. Study young pines and firs, and find out during which
period of life they grow most rapidly.
6. Which trees have you found growing (_a_) in heavy clay
soils, (_b_) in sandy soils?
7. Describe any observations upon six common British trees
which could be made during a walk in early spring. (N.F.U.)