Download Seed Seedling and Plant - Oregon State University

Name and Date _________________________
Section # ______________________________
Lab 3.
Seed, Seedling and Plant;
Tissues and Vegetative Structures
The plant body is composed of two integrated organ systems: the shoot system
and the root system. The shoot system is designed for energy and carbon capture through
photosynthesis, as well as for reproduction. Shoots are composed of stems, leaves and
flowers, which all have a critical function and a unique structure. The root system is
designed for anchorage, storage and the harvesting of both minerals and water from soils.
The root system, too, has structurally different organs designed to fulfill a particular
function. Today in lab you will start by studying the external structure (morphology) of a
whole plant body from embryos in the seed to the development of mature organs systems
in the seedling and mature plant. You will also study the diversity of external form in
plants and novel modifications of stems and leaves.
1. Seed, Seedling and Plant
Choose one of the plants available today in lab to trace the development of the
root and shoot systems from its’
embryonic origin in the seed to fully
developed leaves stems, flowers and
roots in a mature plant.
Seeds contain embryonic shoot
and root axes as well as storage
material for the germinating seedling.
In most dicots this storage occurs in
the fleshy embryonic seed leaves
(cotyledons). In monocots, the
storage material is often in the form of
endosperm and is extra-embryonic
(i.e. found outside of the embryo).
The cotyledon in monocots is often
used to absorb the energy stored in the
endosperm and then passes into the
rapidly growing seedling.
Carefully dissect acorn and bean seed to observe the embryonic axis, cotyledons
and storage materials. Sketch and label the dissected seeds in the space below.
Seedlings show initial developmental forms, which may have several juvenile aspects
to them. When compared to seedlings, mature plants may have very different leaf sizes
or shapes and may show different branching patterns in both the root and shoot system.
In the space below sketch both a seedling and a mature plant. Highlight
developmental differences in leaf, stem and root morphology. Label your drawing.
2. Vegetative Structures
Winter twigs can be used to display
the morphological features found on most
woody stems. Observe the different winter
twigs on display in lab today and compare the
variation in morphological features shared by
each twig. Identify structures such as the
terminal and axillary buds, nodes and
internodes, leaf scars and lenticels. Notice
that these species vary considerably in their
outer appearance. Most shrubs and trees are
unique enough for field identification based
on their twig morphology alone.
In the space below, sketch 2 or 3 terminal
buds and leaf scars from different species.
Identify the species of winter twigs with the
key provided.
Twig #
Species
2
Leaf morphology and arrangement can vary
widely between species of plants. A typical leaf will be
constructed of a blade designed for photosynthesis and
a stem-like structure called the petiole that attaches the
blade to the stem. In the upper notch between the
petiole and the stem is an axillary bud, which is a
dormant shoot and is diagnostic of a leaf. Of course
there are many exceptions to the typical leaf and you
will be looking at the wide variation in leaf types and
morphology in lab today. In the space provided below,
sketch one of the leaves on display in lab today.
Represent as best as you can, leaf characteristics such
as venation, margin type and leaf arrangement.
Observe the different examples of leaf, stem
and shoot morphology on display in lab today. Can
you find examples of different leaf shapes,
arrangements and venation? Use the table below to
organize your observations.
Species
arrangement
Leaf shape
Venation
Leaf margin
3
3. Modifications of Leaves and Shoots
Leaves and shoots are sometimes modified in plants to achieve a variety of
functions. For example, in grapes, peas, cucumbers and many other vines, the blade or
the petiole is modified into a climbing structure called a tendril. Tendrils will wrap
around anything that they touch and thus will allow plants to climb other plants, trellises,
fences, stakes etc. In some cases leaves are modified for protection as is the case of the
spines found on cacti. Spines are modified leaves whereas other structures, such as rose
prickles, are modified from the epidermis and thorns are modified from stems (such as
those on Hawthorns). Carnivorous plants modify their leaves to act as insect traps.
Carnivorous plants generally grow in nutrient poor soils and the trapped insects serve as
an extra source of nitrogen and phosphorus.
Plants will sometimes modify their stems to act as dispersal or over wintering
structures. Stolons are modified stems that run along the surface of the ground and will
produce new plants from the axillary buds at its’ nodes. Rhizomes are underground
stems that can store starch reserves that will be utilized by the growing plant the
following spring. New plants will also arise from the axillary buds located at its’ nodes.
Notice the examples of modified leaves and stems. Fill in the table below with
the name of the modified structure (eg stolon), its developmental origin (e.g. a modified
stem) and its function (e.g. over wintering structure)
Species
Name of
structure
Modified from
what structure
function
4
4. Root Systems
Plant roots systems fall into two general categories: tap root systems and fibrous
root systems. Within each of these architectural types there is tremendous variation in
the extent to which roots branch and the depth to which they penetrate soils. The
categories stem from a developmental
difference which is established shortly
after the species germinates from its
seed. When the embryonic root axis
(primary root) persists and grows into
a strong leader root, a tap root system
develops. On the other hand if the
primary root is short lived and the
root system is dominated by
branching lateral roots, then a fibrous
root system results. In general tap
root systems penetrate deeper into the
soil than fibrous root systems, which
are more likely to dominate in
shallower soil depths.
In many species roots can
become swollen with storage
products, usually starch. Examples of
storage roots that form from tap roots
include carrots, rutabagas and turnips.
It is also common for fibrous roots to store starch as is the case with begonias, dahlias
and sweet potatoes.
Study the root systems made available in today’s lab. Look for the presence of
the primary root and the relative abundance of lateral roots in each plant. Make
representative sketches in the space below. Make sure to label your drawings.
5