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.
[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 centre.]
_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 apricot and pear (Figs. 137, 138).
_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 some of 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.
[Illustration: FIG. 139.—LEAF-SCARS.—Ailanthus.]
_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 length of the
internodes than on the number of leaves.
=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.
[Illustration: FIG. 140.—TERMINAL BUD BETWEEN TWO OTHER
BUDS.—Currant.]
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.
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.
[Illustration: FIG. 142.—FRUIT-BUD OF PEAR.]
[Illustration: FIG. 143.—THE OPENING OF THE PEAR FRUIT-BUD.]
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. 144.—OPENING PEAR LEAF-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.
[Illustration: FIG. 145.—OPENING OF THE PEAR-BUD.]
=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.]
[Illustration: FIG. 149.—FRUIT-BUDS AND LEAF-BUDS OF PEAR.]
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.
_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 centre.]
[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.
=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 the vigour 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 buds 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 the 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 the vigour
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 growth. 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 bud 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 colour 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 the Norway maple. What do
you learn?
[Illustration: FIG. 157.—BUDS OF THE HICKORY.]