WINTER AND DORMANT BUDS
=A bud is a growing point=, terminating an axis either long or short,
or being the starting point of an axis. _All branches spring from
buds._ In the growing season the bud is active; later in the season it
ceases to increase the axis in length, and as winter approaches the
growing point becomes more or less thickened and covered by protecting
scales, in preparation for the long resting season. This resting,
dormant, or winter body is what is commonly spoken of as a “bud.” A
winter bud may be defined as an _inactive covered growing point_,
waiting for spring.
_Structurally, a dormant bud is a_ =shortened axis= _or_ =branch=,
_bearing miniature leaves or flowers or both, and protected by a
covering._ Cut in two, lengthwise, a bud of the horse-chestnut or other
plant that has large buds. With a pin separate the tiny leaves. Count
them. Examine the big bud of the rhubarb as it lies under the ground in
late winter or early spring; or the crown buds of asparagus, hepatica,
or other early spring plants. Dissect large buds of the apple and pear
(Figs. 137, 138).
[Illustration: FIG. 137.--BUD OF APRICOT, showing the miniature leaves.]
[Illustration: FIG. 138.--BUD OF PEAR, showing both leaves and flowers.
The latter are the little knobs in the center.]
_The bud is protected by firm and dry scales._ These scales are
modified leaves. The scales fit close. Often the bud is protected by
varnish (see horse-chestnut and the balsam poplars). Most winter buds
are more or less woolly. Examine them under a lens. As we might expect,
bud coverings are most prominent in cold and dry climates. Sprinkle
water on velvet or flannel, and note the result and give a reason.
=All winter buds give rise to branches=, _not to leaves alone_; that
is, the leaves are borne on the lengthening axis. Sometimes the axis,
or branch, remains very short,--so short that it may not be noticed.
Sometimes it grows several feet long.
_Whether the branch grows large or not depends on the chance it
has_,--position on the plant, soil, rainfall, and many other factors.
The new shoot is the unfolding and enlarging of the tiny axis and
leaves that we saw in the bud. If the conditions are congenial, the
shoot may form more leaves than were tucked away in the bud. The length
of the shoot usually depends more on the lengths of the internodes than
on the number of leaves.
[Illustration: FIG. 139.--LEAF-SCARS.--Ailanthus.]
=Where Buds are.=--_Buds are borne in the_ =axils= _of the leaves_,--in
the acute angle that the leaf makes with the stem. When the leaf is
growing in the summer, a bud is forming above it. When the leaf falls,
the bud remains, and a scar marks the place of the leaf. Fig. 139 shows
the large leaf-scars of ailanthus. Observe those on the horse-chestnut,
maple, apple, pear, basswood, or any other tree or bush.
Sometimes two or more buds are borne in one axil; the extra ones are
=accessory= or =supernumerary= buds. Observe them in the Tartarian
honeysuckle (common in yards), walnut, butternut, red maple, honey
locust, and sometimes in the apricot and peach.
If the bud is at the end of a shoot, however short the shoot, it is
called a =terminal bud=. _It continues the growth of the axis in a
direct line._ Very often three or more buds are clustered at the tip
(Fig. 140); and in this case there may be more buds than leaf scars.
Only one of them, however, is strictly terminal.
[Illustration: FIG. 140.--TERMINAL BUD BETWEEN TWO OTHER
BUDS.--Currant.]
A bud in the axil of a leaf is an =axillary= or =lateral= bud. Note
that there is normally at least one bud in the axil of every leaf on a
tree or shrub in late summer and fall. The axillary buds, if they grow,
are the _starting points of new shoots the following season_. If a leaf
is pulled off early in summer, what will become of the young bud in its
axil? Try this.
[Illustration: FIG. 141.--A GIGANTIC BUD.--Cabbage.]
_Bulbs and cabbage heads may be likened to buds_; that is, they are
condensed stems, with scales or modified leaves densely overlapping and
forming a rounded body (Fig. 141). They differ from true buds, however,
in the fact that they are condensations of whole main stems rather than
embryo stems borne in the axils of leaves. But bulblets (as of tiger
lily) may be scarcely distinguishable from buds on the one hand and
from bulbs on the other. Cut a cabbage head in two, lengthwise, and see
what it is like.
The buds that appear on roots are unusual or abnormal,--they occur only
occasionally and in no definite order. Buds appearing in unusual places
on any part of the plant are called =adventitious buds=. Such usually
are the buds that arise when a large limb is cut off, and from which
suckers or water sprouts arise.
[Illustration: FIG. 142.--FRUIT-BUD OF PEAR.]
[Illustration: FIG. 143.--THE OPENING OF THE PEAR FRUIT-BUD.]
[Illustration: FIG. 144.--OPENING PEAR LEAF-BUD.]
[Illustration: FIG. 145.--OPENING OF THE PEAR-BUD.]
=How Buds Open.=--_When the bud swells, the scales are pushed apart,
the little axis elongates and pushes out._ In most plants the outside
scales fall very soon, _leaving a little ring of scars_. With terminal
buds, this ring marks the end of the year’s growth: how? Notice peach,
apple, plum, willow, and other plants. In some others, all the scales
grow for a time, as in the pear (Figs. 142, 143, 144). In other plants
the inner bud scales become green and almost leaf-like. See the maple
and hickory.
=Sometimes Flowers come out of the Buds.=--Leaves may or may not
accompany the flowers. We saw the embryo flowers in Fig. 138. The bud
is shown again in Fig. 142. In Fig. 143 it is opening. In Fig. 145 it
is more advanced, and the woolly unformed flowers are appearing. In
Fig. 146 the growth is more advanced.
[Illustration: FIG. 146.--A SINGLE FLOWER IN THE PEAR CLUSTER, as seen
at 7 A.M. on the day of its opening. At 10 o’clock it will be fully
expanded.]
[Illustration: FIG. 147.--THE OPENING OF THE FLOWER-BUD OF APRICOT.]
[Illustration: FIG. 148.--APRICOT FLOWER-BUD, enlarged.]
Buds that contain or produce only leaves are =leaf-buds=. Those which
contain only flowers are =flower-buds= or =fruit-buds=. The latter
occur on peach, almond, apricot, and many very early spring-flowering
plants. The single flower is emerging from the apricot bud in Fig. 147.
A longitudinal section of this bud, enlarged, is shown in Fig. 148.
Those that contain both leaves and flowers are =mixed buds=, as in
pear, apple, and most late spring-flowering plants.
[Illustration: FIG. 149.--FRUIT-BUDS AND LEAF-BUDS OF PEAR.]
_Fruit buds are usually thicker or stouter than leaf-buds. They are
borne in different positions on different plants._ In some plants
(apple, pear) they are on the ends of short branches or spurs; in
others (peach, red maple) they are along the sides of the last year’s
growths. In Fig. 149 are shown three fruit-buds and one leaf-bud on
_E_, and leaf-buds on _A_. See also Figs. 150, 151, 152, 153, and
explain.
[Illustration: FIG. 150.--FRUIT-BUDS OF APPLE ON SPURS: a dormant bud
at the top.]
[Illustration: FIG. 151.--CLUSTER OF FRUIT-BUDS OF SWEET CHERRY, with
one pointed leaf-bud in center.]
[Illustration: FIG. 152.--TWO FRUIT-BUDS OF PEACH with a leaf-bud
between.]
[Illustration: FIG. 153.--OPENING OF LEAF-BUDS AND FLOWER-BUDS OF
APPLE.]
“_The burst of spring_” means in large part the opening of the buds.
_Everything was made ready the fall before. The embryo shoots and
flowers were tucked away, and the food was stored._ The warm rain
falls, and the shutters open and the sleepers wake: the frogs peep and
the birds come.
=Arrangement of Buds.=--We have found that leaves are usually arranged
in a definite order; buds are borne in the axils of leaves: therefore
_buds must exhibit phyllotaxy_. Moreover, branches grow from buds:
branches, therefore, should show a definite arrangement; usually,
however, they do not show this arrangement because _not all the buds
grow and not all the branches live_. (See Chaps. II and III.) It is
apparent, however, that the mode of arrangement of buds determines to
some extent the form of the tree: compare bud arrangement in pine or
fir with that in maple or apple.
[Illustration: FIG. 154.--OAK SPRAY. How are the leaves borne with
reference to the annual growths?]
The uppermost buds on any twig, if they are well matured, are usually
the larger and stronger and they are the most likely to grow the next
spring; therefore, branches tend to be arranged in tiers (particularly
well marked in spruces and firs). See Fig. 154 and explain it.
=Winter Buds show what has been the Effect of Sunlight.=--Buds are
borne in the axils of the leaves, and the size or vigor of the leaf
determines to a large extent _the size of the bud._ Notice that, in
most instances, _the largest buds are nearest the tip_ (Fig. 157). If
the largest ones are not near the tip, there is some special reason for
it. Can you state it? Examine the shoots on trees and bushes.
[Illustration: FIG. 155.--AN APPLE TWIG.]
[Illustration: FIG. 156.--Same twig before leaves fell.]
SUGGESTIONS.--Some of the best of all observation lessons are those
made on dormant twigs. There are many things to be learned, the eyes
are trained, and the specimens are everywhere accessible. =123.=
At whatever time of year the pupil takes up the study of branches,
he should look for three things: the ages of the various parts,
the relative positions of the buds and leaves, the different sizes
of similar or comparable buds. If it is late in spring or early in
summer, he should watch the development of the buds in the axils,
and he should determine whether the strength or size of the bud
is in any way related to the size and vigor of the subtending (or
supporting) leaf. The sizes of buds should also be noted on leafless
twigs, and the sizes of the former leaves may be inferred from the
size of the leaf-scar below the bud. The pupil should keep in mind
the fact of the struggle for food and light, and its effects on the
developing buds. =124.= _The bud and the branch._ A twig cut from
an apple tree in early spring is shown in Fig. 155. The most hasty
observation shows that it has various parts, or members. It seems to
be divided at the point _f_ into two parts. It is evident that the
part from _f_ to _h_ grew last year, and that the part below _f_ grew
two years ago. The buds on the two parts are very unlike, and these
differences challenge investigation.--In order to understand this
seemingly lifeless twig, it will be necessary to see it as it looked
late last summer (and this condition is shown in Fig. 156). The part
from _f_ to _h_,--which has just completed its growth,--is seen to
have its leaves growing singly. In every axil (or angle which the
leaf makes when it joins the shoot) is a bud. The leaf starts first,
and as the season advances the bud forms in its axil. When the leaves
have fallen, at the approach of winter, the buds remain, as seen
in Fig. 155. Every bud on the last year’s growth of a winter twig,
therefore, marks the position occupied by a leaf when the shoot was
growing.--The part below _f_, in Fig. 156, shows a wholly different
arrangement. The leaves are two or more together (_aaaa_), and there
are buds without leaves (_bbbb_). A year ago this part looked like
the present shoot from _f_ to _h_,--that is, the leaves were single,
with a bud in the axil of each. It is now seen that some of these
bud-like parts are longer than others, and that the longest ones are
those which have leaves. It must be because of the leaves that they
have increased in length. The body _c_ has lost its leaves through
some accident, and its growth has ceased. In other words, the parts
at _aaaa_ are like the shoot _fh_, except that they are shorter, and
they are of the same age. One grew from the end or terminal bud of
the main branch, and the others from the side or lateral buds. Parts
or bodies that bear leaves are, therefore, branches.--The buds at
_bbbb_ have no leaves, and they remain the same size that they were
a year ago. They are dormant. The only way for a mature bud to grow
is by making leaves for itself, for a leaf will never stand below it
again. The twig, therefore, has buds of two ages,--those at _bbbb_
are two seasons old, and those on the tips, of all the branches
(_aaaa_, _h_), and in the axil of every leaf, are one season old. It
is only the terminal buds that are not axillary. When the bud begins
to grow and to put forth leaves, it gives rise to a branch, which, in
its turn, bears buds.--It will now be interesting to determine why
certain buds gave rise to branches and why others remained dormant.
The strongest shoot or branch of the year is the terminal one (_fh_).
The next in strength is the uppermost lateral one, and the weakest
shoot is at the base of the twig. The dormant buds are on the under
side (for the twig grew in a horizontal position). All this suggests
that those buds grew which had the best chance,--the most sunlight
and room. There were too many buds for the space, and in the struggle
for existence those that had the best opportunities made the largest
growths. This struggle for existence began a year ago, however,
when the buds on the shoot below _f_ were forming in the axils of
the leaves, for the buds near the tip of the shoot grew larger and
stronger than those near its base. The growth of one year, therefore,
is very largely determined by the conditions under which the buds
were formed the previous year. _Other bud characters._ =125.= It is
easy to see the swelling of the buds in a room in winter. Secure
branches of trees and shrubs, two to three feet long, and stand them
in vases or jars, as you would flowers. Renew the water frequently
and cut off the lower ends of the shoots occasionally. In a week or
two the buds will begin to swell. Of red maple, peach, apricot, and
other very early-flowering things, flowers may be obtained in ten to
twenty days. =126.= The shape, size, and color of the winter buds
are different in every kind of plant. By the buds alone botanists
are often able to distinguish the kinds of plants. Even such similar
plants as the different kinds of willows have good bud characters.
=127.= Distinguish and draw fruit-buds of apple, pear, peach, plum,
and other trees. If different kinds of maples grow in the vicinity,
secure twigs of the red or swamp maple, and the soft or silver maple,
and compare the buds with those of the sugar maple and Norway maple:
What do you learn?
[Illustration: FIG. 157.--BUDS OF THE HICKORY.]