Agriculture Reference
In-Depth Information
Apical bud encased in
bud scales
Axillary bud
developing into
lateral branch
Node
Internode
Axillary bud
Horseshoe shaped
leaf scar - 'nails'
are the vascular
connections to
the old leaf
Lenticels
Bud scale (girdle)
scar - last season's
apical bud
Figure 7.4 External features of a woody stem in Aesculus hippocastanum (horse chestnut)
spring. The Aesculus hippocastanum (horse chestnut)
buds shown in Figure 7.4, for example, exude a sticky
substance to deter insects. A terminal (apical) bud
is present at the tip of a main stem or branch and
contains a meristem from which lengthwise vegetative
growth or, less commonly, a flower will emerge.
Where leaves join the stem, axillary buds may grow
into lateral shoots or flowers or may remain dormant.
Bud characteristics may be useful in identifying
plants - for example, the native ash Fraxinus excelsior
has black buds, those of beech ( Fagus sylvatica ) are
long and pointed and Magnolia buds are hairy (Figure
7.10a-c). Flowering buds tend to be much larger and
plumper than the vegetative buds (Figure 7.10d),
which give rise to new shoots and leaves and this is
useful when pruning. In spur pruning of apples, for
example, the vegetative buds on the ends of lateral
shoots are easily identified and removed encouraging
development of flower buds.
the stem depending on the water and light energy
supply in the species' habitat. Sessile leaves lack a
petiole, while in peltate leaves such as Nasturtium ,
the petiole attaches to the centre of the lamina rather
than the base (Figure 7.11d). Many monocotyledonous
leaves also lack a petiole.
Leaf shape and structure (Figure 7.11) are useful
indicators when attempting to identify a plant and
descriptions often include specific terms. A few
are described below but many more are used by
botanists:
X Simple leaves have a continuous leaf blade, with
an axillary bud at the base of the petiole (Figure
7.11a-f). There are a multitude of leaf shapes,
e.g. lanceolate, ovate, obovate, lobed, orbicular
and oval. Linear leaves are characteristic of
monocotyledons (Figure 7.11a).
X Compound leaves, notably compound palmate
and compound pinnate, have separate leafl ets each
with an individual base on one leaf stalk, but the
only axillary bud is at the base of the main leaf stalk
where it attaches to the stem (Figure 7.11g and h).
X Margins of leaves can be described, for example,
as entire (unbroken or smooth) (Figure 7.11e),
sinuous, serrate, dentate or crenate.
Leaves
The main function of the leaf is to carry out
photosynthesis .
The leaf consists of the leaf blade ( lamina ) and stalk
( petiole ) (Figure 7.2), its shape and arrangement on
 
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