Transcript Stems and Leaves

Primary Growth:
•Apical
Meristem – the main upward growth
shoot of a tree or other plant.
The Axillary Bud is
the “insurance policy”
that takes over if the
original apical
meristem is lost and
becomes the new
apical meristem. They
can also form
branches or flowers.

When the original apical meristem is
damaged, a new axillary bud takes over and
creates a new apical meristem.
New Apical Meristem
already formed

The Lateral Meristem is the outward growth
area of a plant. A woody plant leaves behind
rings where this happens. These rings can be
counted to determine the age of the plant.
This tree, for example
is 6 years old. It is
important to remember
to count the pith and
the outer cambium
layer.

The meristem at the bottom of roots is also called
an apical meristem. This is where we get a lot of
the information we have about plant growth and
development, due to it’s ease of study.


Phylotaxis is the arrangement of leaves on a
plant. They may be simple, or more complex.
Road Trip (sort of!) Let’s look at some simple
leaves; pinnate; bi-pinnate, and palmate leaves
and then go out on the campus to locate
examples of each!
Lobes
Simple leaves always
have a single blade
attached to the petiole.
It is important to
remember that leaves
DO NOT have stems!
Blade
Petiole
Pinnate leaves
are once
divided along
the leaf petiole
and rachis.
Hickory is a
good example
of this.
Bipinnate
leaves are
twice
divided
along the
leaf petiole
and rachis.
Mimosa is a
good
example of
this.
Palmate
leaves have
leaflets that
spread
outward like
the fingers of
a hand, often
in palms and
other plants.
In Perfoliate leaves, the stem
perforates the new leaves that
develop around it. Honeysuckle is
a really good example.
Peltate
leaves are
attached by
the petiole
directly to
the center of
the blade of
the leaf.
Example :
lily pads
A peltate leaf
looks like this
underneath.
I couldn’t find
a photo that
showed this!
nodes
Note that the
leaves are
opposite each
other on the
branch at each
node. A node is
where leaves or
flowers emerge
from the branch.
Example : Red
Maple
In alternate
arrangement,
the leaves or
flowers will
be arranged
on the branch
at the nodes
in a pattern
alternating
from one side
to the other.
nodes
Example: Persimmon
In a whorled
leaf
arrangement,
the leaves
radiate out
from a single
node. There
may be many
of them or
just a few.
Sinningia leucotricha
Net
venation
spreads
out from
the rachis
like the
branches
of a tree.
Examples:
sycamore;
maple
In parallel
venation, the
veins move
along the blade
in a parallel
fashion, never
spreading or
branching.
Example: corn
Is this leaf,
simple or
compound?
What kind of venation is
displayed here?
What kind of
leaf
arrangement
do we see
here?