Plant Anatomy -
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Plant Anatomy
A plant is a member of the kingdom Plantae, a living organism that utilizes photosynthesis, a process in which energy from sunlight is converted to chemical energy (food).
Plants are at the base of the food web and are autotrophs (or producers - organisms that make their own food).
Plants vary greatly in size, shape, and the type of environment in which they live.
Structure and Function: Roots anchor the plant in the ground and absorb water and mineral nutrients from the ground.
Leaves contain chloroplasts, in which photosynthesis occurs.
Carbon dioxide is absorbed through oxygen is produced as a byproduct of photosynthesis and is released.
Plant cells have a supportive cellulose cell wall (unlike animal cells which lack cellulose).
The following is a diagram of the external anatomy of a typical flowering plant:
axil - the angle between the upper side of the stem and a leaf, branch, or petiole.
axillary bud - a bud that develops in the axil.
flower - the reproductive unit of .
flower stalk - the structure that supports the .
internode - the area of the stem between any two adjacent nodes.
lateral shoot (branch) - an offshoot of the stem of a plant.
leaf - an outgrowth of a plant that grows from a node in the stem.
Most leaves a their main function is to convert energy from sunlight into chemical energy (food) through photosynthesis.
node - the part of the stem of a plant from which a leaf, branch,
each plant has many nodes.
Label the two lower nodes (the first and second nodes) on the plant diagram.
petiole - it attaches the leaf to the plant.
root - a root is a plant structure that obtains food and water from the soil, stores energy, and provides support for the plant.
Most roots grow underground.
root cap - a structure at the ends (tips) of the roots.
It covers and protects the apical
(the actively growing region) of the root.
stem - (also called the axis) is the main support of the plant.
tap root - the main the tap root extends straight down under the plant.
terminal bud - a bud located at the apex (tip) of the stem.
Terminal buds have special tissue, called , consisting of cells that can divide indefinitely.
Phyla: The phyla in the kingdom Plantae include:
Ginkgophyta, Lycophyta (lower ferns like club mosses), Pterophyta (ferns), Psilophyta (whisk ferns),
(flowering plants), Gnetophyta, Sphenophyta, Coniferophyta (conifers), Cycadophyta (cycads), Sphenophyta, and
(mosses, liverworts, hornworts).
Botany and Paleobotany Dictionary
Click on an underlined word for more information on that subject.
If the plant term you are looking for is not in the dictionary, please .
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©2000The word Iris means rainbow. Iris is the flower of the Greek goddess Iris who is the messenger of Love. In the language of flowers Iris symbolizes eloquence.
Irises are wonderful garden plants. The word Iris means rainbow. Irises come in many colors such as blue and purple, white and yellow, pink and orange, brown and red, and even black.
The genus Iris has about 200 species and is native to the North Temperate regions of the world. The habitat of irises also varies a lot. Some irises grow in deserts, some in swamps, some in the cold far north, and many in temperate climates. Bearded Iris and Siberian Iris are two of the most common types of irises grown.
Magnoliophyta
Liliopsida
Asparagales
Since Iris is the Greek goddess for the Messenger of Love, her sacred flower is considered the symbol of communication and messages. Therefore the flower iris in the language of flowers symbolizes eloquence. Based on their color, irises convey varied messages. A purple iris is symbolic of wisdom and compliments. A blue iris symbolizes faith and hope. A yellow iris symbolizes passion while white iris symbolizes purity. A gift of iris can be used to convey many emotions.
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Some Interesting Facts about Iris
Irises come in many forms, shapes, colors and sizes and the sword-like foliage is attractive when the plant is not in bloom.
The Iris was named after the Greek goddess who is considered to be the messenger of love and uses the rainbow to travel. Iris was probably named after the goddess because of the numerous colors it is available in.
Irises are among the best-known and loved among garden plants. Irises are hardy herbaceous perennials.
The genus Iris is a large genus of
and rhizomatous perennials.
The Iris was named after the goddess of the rainbow because of its many colors.
A flower on the Sphinx is considered to be an Iris, and another appears on a bas-relief of the time of the 18th Egyptian dynasty.
Pliny also knew the Iris and praised its medicinal virtues.
The Iris was also a favorite flower of the Moslems who took it to Spain after their conquest in the 8th century.
The Iris flower's characteristic feature is having three petals often called the &standards& and three outer petal-like sepals called the &falls&.
Types of Irises
Irises are classified into two major groups, Rhizome Irises and Bulbous Irises. Within those groups are countless species, varieties, cultivars and hybrids, according to the American Iris Society.
Rhizome Irises are thickened stems that grow horizontally, either underground or partially underground. After planting, iris rhizomes produce sword like leaves that overlap, forming flat fans of green foliage. Three popular irises in this group are Bearded, Beardless and Crested Irises.
The bearded iris has four distinct parts: the Standards, Falls, Stigma flaps, and Beard
The beardless variety has: Standards, Falls and Stigma flaps, but usually have crests
The crested Irises or Evansia Iris has: Standards, Falls and Stigma flaps and in addition to a ridge on the falls of the blossom, they have ridges like crests instead of beards
Crested irises are often considered in the same manner as the beardless iris. These plants spread freely by underground stems and produce flat flowers in the shades of blue, violet and white. Often the flowers and leaves are found on bamboo like stems which can vary in height from 5-200 centimeters in height.
Bulbous irises grow from bulbs that require a period of dormancy after they have bloomed. The bulbous irises are typically smaller than rhizome irises and usually produce smaller blossoms.
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Growing Irises
Before planting Iris, improve the soil conditions by using a slow release fertilizer. To increase the organic matter content, use compost, peat moss or well-rotted manure. Fertilizer and organic matter should be worked thoroughly into the top 4 to 6 inches of soil.
Wooded areas with good drainage and partial shade are ideal spots for the crested iris.
Irises are grown from both seed and root separation.
The roots or rhizomes, are easily separated and replanted.
The rhizome looks like a long, thin potato with roots underneath.
When transplanting, separate the rhizome. Make sure to have some root and a leaf or two in each section.
Plant the rhizomes near the surface with the roots below.
Divide the clumps and plant single rhizomes, spacing them 8 to 18 inches apart according to the effect desired.
Spade a planting hole about 10 inches deep and work 1 tablespoonful of fertilizer into the soil in the bottom of the hole.
If the soil is heavy, some drainage material such as gravel or broken pottery should be placed in the hole.
Fill the hole with loose soil and place the root section so that it will not be covered more than 1 inch deep.
Most Beardless Irises can also be propagated from seeds.
The Dykes Medal is awarded annually to the finest iris of any class. Tall bearded irises have won the Dykes Medal more often than any other class.
Iris Plant Care
Apply a thin layer of compost around the base of plants each spring, leaving the rhizome exposed.
As flowers fade, cut back the flower stalks to the base of the plant.
To encourage a second bloom on re-blooming varieties, promptly remove faded flowers and maintain consistent watering throughout the summer.
In autumn, trim away dead foliage and prune back healthy leaves to a height of 4 to 5 inches.
Once the soil has frozen, apply a layer of mulch to help prevent roots from heaving out of the soil during alternate freezing and thawing.
If heaving occurs, don't try to force plants back into the soil. Instead, cover rhizomes and exposed roots with soil.
Divide bearded irises every 4 to 5 years, preferably in late summer. Each division should have one or two leaf fans. Older rhizomes that have few white feeding roots should be discarded.
Want to learn more about growing Irises and other flowers?
Other Uses of Iris
The juice of the fresh roots of Iris, bruised with wine, has been employed as a strong purge of great efficiency in dropsy.
Iris roots are used to treat skin diseases. The juice of Irises are also sometimes used as a cosmetic for the removal of freckles on the skin.
The fresh root of the Iris germanica is a powerful cathartic, and for this reason its juice has been employed in dropsy. It is chiefly used in the dry state, being said to be good for complaints of the lungs, for coughs and hoarseness, but is now more valued for the pleasantness of its violet-like perfume than for any other use.
Iris flowers are used as a liver purge.
Purple Iris
Purple Iris Flowers bloom for two to three weeks in the late spring to early summer.
The Purple Iris is the state flower of Tennessee.
The Purple Iris can be grown in your home, in containers.
The majority of Iris flowers are in Purple.
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此题重点考查生物知识，胡萝卜是根而不是花，也不是叶子。
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扫描下载二维码4 - Flower Plants (Phanerogams)
Flowering Plants (Phanerogams)
Giorgio Carboni, April 2007
Translated by Sarah Pogue
Figure 1 – Ovule of white campion flower (Silene
latifolia).
Detail of figure 14. Ovule dimension = 1 mm.
In the previous article, we dealt with the “inferior”
terrestrial plants, those plants which reproduce by means of spores and are
called Cryptogams. In the present article, we will look at the “superior”
terrestrial plants, or more exactly, the
Phanerogams. These are vascular
plants that have flowers and produce seeds. The terms Spermatophyte (from the
Greek: spèrmatos = phytòn = plant), Phanerogam (faneròs = gàmos =
marriage) and Anthophyte (from àntos = flower) are synonymous. These include the
Gymnosperms (plants with flowers and unenclosed ovules: conifers and other minor
families) and the Angiosperms (plants with flowers and closed ovaries: the most
common plants).
In contrast to the Cryptogams, which are relatively primitive
plants, the
Phanerogams and in particular the Angiosperms are plants that
have undergone a notable evolution and which have a wide variety of specialised
tissues and organs such as roots, stems, leaves, flowers etc.
The flowers are without doubt the most striking and beautiful parts of the
plant, and it is with these that we will begin our explorations. Now, think of a
flying insect that catches sight of a flower, changes direction, lowers its
altitude and as it approaches detects an intoxicating perfume as the petals seem
to open up to reveal a landing strip. The insect lands and goes towards a
perfumed coloured chamber where it finds nectar and pollen. The encounter with
the flower will be a fascinating experience also for us. Unfortunately, we
cannot taste the nectar, but the colours and the shapes that we can admire are
certainly delightful, particularly if we observe them under the microscope.
During the spring, in fields and gardens, you can collect an
infinite number of flowers to examine. You mustn’t think that when observing a
flower under the microscope you can see the same things as when you look at it
with the naked eye only bigger, because flowers almost always reveal unexpected
details when viewed with a microscope which are very beautiful and of great
Take for example the heartsease or wild pansy (Viola
tricolor, Figure 2). You will have noticed how its petals are velvety. With the
stereoscopic microscope, it is possible to note that the petals are covered with
finger-like cells called papillae (Figure 3). The papillae are what makes the
petals of the pansy particularly velvety to the touch. The height of these
“fingers” grows as you move towards the interior of the flower and when you are
close to the gynoecium or pistil these suddenly reach a length of several
millimetres and are called hairs (Figure 4). Thanks to these finger-like
structures and their colours, the observation of the pansies is particularly
striking. There are different species of pansy and it is certainly interesting
to observe the differences between them.
Figure 2 – Flower of heartsease/wild pansy.
Figure 3 - Papillae from the upper surface of the petal.
Passo = Distance between papillae = 0.02 mm.
Figure 4 – Hairs close to the pistil.
Figure 5 – Hairs of the pansy viewed under
biological microscope. Diameter = 0.14 mm
Figure 6 – Nuclei of pansy hairs.
Figure 7 – Cells from the lower surface of
the petal.
With a pair of fine tweezers, remove a piece of tissue from a
petal where the “fingers” are longest and observe it under the biological
microscope (Figure 5). Obviously, in order to do this, you must immerse the
strip in water, then place it between two microscope slides and add some drops
of alcohol to disperse any air bubbles present. You will realise that these
hairs are none other than single cells and you will also see their nucleus
(Figure 6). The papillae that cover the petal and that give it its velvety
aspect and texture are cells and on every petal there are tens of thousands of
these (Figure 3). Obviously, each cell has its nucleus and this is normal, but
it makes us reflect on the complexity and perfection of biological structures.
If necessary, colour the strip with a dye for chromatin in order to make the
nuclei more evident.
Remove the strip of the epidermis from the underside of the
petal and look at it under the microscope. You will see that the single cells of
this tissue have a shape that reminds us of jigsaw pieces (Figures 7 and 41). Often the
flowers, but also the leaves, possess cells of this shape which allow the plant
to increase the surface area of contact between the cells.
Figure 8 – Diagram of a flower.
Figure 9 - Campanula flower (Campanula
Now we will move on to a more detailed examination of the
flowers in which we will seek to understand their form and organisation. We will
begin with the examination of simple flowers in which it is easy to distinguish
the four principal parts: sepals, petals, stamens and pistil (Figure 8). Flowers
suitable for this examination are the campanula (Figure 9), ranunculus, dianthus
and many others. Many other flowers, amongst which is the violet, are not
well-suited for this initial observation because their organs are highly
modified with repect to the “basic” structure and it would be difficult to
recognise them. Further on, when you are familiar with the wide variety of
botanical structures, you can also examine these flowers.
Now, arm yourself with tweezers and a scalpel and, under the
stereoscopic microscope, section the flower to analyse its parts:
- remove a couple of petals to uncover th
- remove a stamen and observe the anther and the pol
- examine the various parts of the pistil: ovary, style, stigma. In the
campanula the stigma is divi
- look and see if there are pollen
- section the pistil longitudinally, examine the ovary, the placement of the
ovules and their
- observe the contour of the petals and their upper and lower surfaces, describe
any hairs present and any o
- observe the sepals, especially any h
- describe any insects present on the flower.
With a biological microscope:
- observe the pollen at
- remove a strip from the upper and lower surfaces of the petal to observe the
- make transverse se
- observe any hairs present on the petals and sepals.
During this anatomical exam, it would also be useful to make
a drawing or a diagram of the sectioned flower and to write a brief report
accompanied by drawings and photos. At the end you could collect all the
drawings, photos, reports and preserved specimens in a file. These documents
will be very useful for comparative examinations of the flowers of different
After studying the flowers of different plants, you will
realise that the differences regard not only the colour, but also and above all
the structure. In fact, during the course of evolution, the “basic” form of the
primitive flowers has greatly diversified and the study of these is now
particularly interesting. For example, think of the daisy which is formed of
hundreds of miniscule flowers, each of which is equipped with stamens and
pistil. These flowers are arranged in spirals on the flower head. It is not by
chance that these flowers are called Composites. The flower head is the
structure composed of all the small flowers. With regard to the terminology, it
is incorrect to call the flower head of a Composite a flower and instead this
must be called an inflorescence or a flower head or better a
capitulum.
Figure 10 – Chicory inflorescence
(Cichorium intybus).
Figure 11 – Chicory floscule: note the
down, the stigma, the blue anthers and the petal.
Figure 12 – Stigma of a chicory
inflorescence.
Numerous white pollen grains are visible.
Chicory is also a composite, even though the number of
flowers of which the inflorescence is composed is inferior to that of the daisy.
In summer, chicory is very common in fields and along the roadside. Its azure
inflorescences are highly visible (Figure 10). As with other composites, the
petal edges are serrated. Sectioning the inflorescence of a chicory plant, you
can ascertain that each of its small flowers has a corolla consisting of a
single petal. This little flower is called a floscule (Figure 11). At its base
is the ovary which contains a single ovule that will become an achene (a dry
fruit containing a single seed). The anther is formed from the fusion of 5
elements, is tubular, blue in colour and wrapped around the pistil. From the
anther the Aries-shaped stigma protrudes, upon which numerous white pollen
grains are visible (Figure 12). While you look at the interior of the
inflorescence you may see some tiny insects peeping out from amongst the
these will most likely be thrips, whose feathery wings you should
also observe.
Observing the inflorescence of chicory, this humble and
common plant, and admiring the spectacle offered by its corolla, you will
realise how nature is full of wonders that don’t cost anything. All you need is
a stereoscopic microscope, at times even just a magnifying lens, to admire the splendid forms
that nature tirelessly produces. This is how a flowering field which, to an
ordinary person doesn’t offer anything in particular, to a microscopist appears
instead as a source of infinite wonder.
Another interesting flower is the white campion (Silene
latifolia), a plant that flowers between May and November. As you can see in
the figures below, the calyx of this flower has the shape of a flask from which
a crown of white petals emerges. This species is dioecious, that is, the male
and female reproductive organs are on separate plants so that on one plant you
will find flowers with the pistil and on another flowers with the stamens. The
male flowers have a narrow calyx and from this the anthers emerge, the female
flowers have a swollen calyx due to the presence of the ovary and from this the
stigmas emerge (Figures 13, 14 and 15).
Figure 13 – Female white campion flower (Silene
latifolia). During maturation, the ovary swells.
Figure 14 – White campion ovary (with
calyx) sectioned.
Diameter approximately 16 mm. See details in figure 1.
Figure 15 – Male white campion flower. On
the right, the
open flower. Note the stamens and the absence of the ovary.
- Collect the female flowers of the white campion at different
- take a female flower that still has petals (Figure 13);
- with a razor blade, remove the calyx and expose the ovary. Note that the
petals depart from the base of the ovary and note also th
- section the swollen ovary longitudinally and observe the ovules (Figure 1 and
- take a male flower. With a small pair of scissors, open the calyx and if
necessary remov
- observe the stamens, the anthers and the pollen. Note the absence of the
After the “basic” flower such as that depicted in Figure 8, I
presented the flower of the campanula, one of the composites and the flower of a
dioecious plant, in order to prepare you for the diversity of flower structure
before leaving you to continue your observations alone.
EXPERIMENTS ON
POLLEN GERMINATIONThe flower stigma is often sticky due to the presence of sugary substances.
Inserting pollen grains in a sugary solution, it is possible to provoke the
emission of the pollen tube. The concentration of sugar in this solution
should be between 2 and 20%, according to the species from which the pollen
derives. In the majority of cases, a concentration of 10% is fine, but for
the Composites it should be from 30 to 45%. Boil some water with sugar added
and prepare some microscope slides for Van Tieghem observations. Another
observation method is that of inserting the pollen grains and solution
between normal microscope slides. If the grains are big, it will be
necessary to insert some pieces of broken coverslip between the slide and
the coverslip, in such a way as to avoid squashing them. Every so often it
will be necessary to add a little water to the solution as it evaporates.
Some texts suggest adding a little gelatine to the solution (approximately
2%). After boiling the solution to sterilise and homogenise it, it will be
necessary to keep it in a bain-marie at 25°C to keep it fluid, then place a
thin film of fluid on some clean sterile microscope slides. On this film
place some pollen grains, even of different species, and keep them in a
humid environment, such as in a Petri dish or in a small shallow glass jar
containing a strip of paper soaked in water. The emission of the pollen tube
can take many hours and will not necessarily happen. In the case that the
emission does take place, you could try to highlight the three nuclei that
are emitted in the tube with a chromatin colourant such as Toluidine blue or
Methylene blue. It is possible to experiment with different concentrations
of the sugary solution to adapt it to different plant species. The pollen of
the plant commonly known as &busy lizzy& (Impatiens sultani or
Impatiens walleriana), emits tubes in less than an hour in a 10% glucose
solution. In the interior of the pollen tube it is also possible to observe
the cytoplasmic currents.
Figure 16 –
Grain of pollen from the lesser celandine
(Ranunculus ficaria) which has produced a pollen tube.
Kept in a 15% sugar solution for approximately 6 hours.
Phase contrast. Field = 0.25 mm.
The flower is a specialised structure of the Spermatophytes
dedicated to sexual reproduction. The fertilised flower is destined to undergo a
transformation which generally leads to the formation of fruit and seeds. The
fruit develops from the lower wall of the pistil (ovary) while the seed
develops from the fertilised ovule.
That which we consider to be the fruit and which represents the
edible part of, for example, an apple, in botany is not considered as the true
fruit since it develops from the receptacle (tissue found at the base of the
flower). In botany, the structure derived from the ovary is considered to be the
fruit, which protects the seeds and which in an apple corresponds to the core.
Often, during maturation, the ovary and the style transform
significantly. Section the ovary at different stages of maturity and try to
follow the development of the fruit, observe the development of the seeds and
the mechanism for their dispersal. Look at, for example, a pumpkin cut in two.
In the lower part you will see what remains of the flower, in the upper part the
petiole of the pumpkin which at one time supported the flower, and in the
central cavity the ovules by now transformed into seeds. All the rest of the
pumpkin is a transformation of the ovary. Analysing the seeds, it will be
possible to distinguish the embryo with its cotyledons,
endosperm, reserve tissue that surrounds and provides nutrition for the
embryo, and the external integument. The text indicated in [404] is a
guide to the spontaneous flowers and is very well illustrated. Besides the
entire plants, it shows details regarding the flowers and fruits which can aid
you in understanding their structure.
The carpel is a leaf that during the evolution of the
Angiosperms transformed into the ovary. The pistil can be formed from one or
more carpels. Fruit can be simple (e.g. peach), aggregate (e.g. raspberry) or
multiple (e.g. pineapple). The fruit can be fleshy or dry. Do not expect,
therefore, for the fruit to always be similar to an apple, as it could also be a
pod as in the case of the bean, a winged achene like the maple etc. Examine and
describe the fruits and seeds of different plants (e.g. Figures 17, 18, 19, 20,
21, 24 and 42). In doing this, it will be useful to you to familiarise yourself
with the botanical classification of fruits and the terminology which you can
find in a biology textbook [001] or in a botanical atlas [003] and [004].
Figure 17 – Oat seeds.
Figure 18 – Shepherd’s purse ovary opened
the ovules. The ovary is approximately 4 mm in width.
Figure 19 – Seeds of thale cress contained
in siliqua
capable of launching them a significant distance.
Figure 20 – Poppy ovaries and seeds.
Figure 21 – Poppy seeds under grazing
Note their kidney-shaped appearance. L = 0.7 mm.
Figure 22 – Sow thistle (Sonchus
oleraceus)
seed tufts. Diameter = 24 mm approximately.
A beautiful ovary to examine is that of the poppy. This has the
shape of a covered jar (Figure 20) and is called a capsule. Above the ovary you
can see the stigmas which are united to form a slightly rounded disc. When the
ovary is mature, small windows open under the disc through which the seeds can
exit. Collect a mature poppy ovary and beat it against the palm of your hand so
that many of the small seeds come out (Figure 20). Examine the ovaries and
section them to study their form and the arrangement of the seeds. Under the
microscope, the poppy seeds show their alveolar kidney-shaped form (Figure 21).
The wild pansy produces a fairly simple ovary which at a certain point opens in
three parts letting the seeds fall. Oat seeds are equipped with two long
appendages which contort when dried so that the seed falls to the earth
penetrating it by rotating about themselves. The petunias instead produce small
utricles that release miniscule seeds when overturned.
Nature produces seeds in such a variety of forms that you
could even create a “herbarium” composed exclusively of seeds. If you prefer,
this collection could be composed only of photographs and, why not, of drawings.
Observe the plant seeds and describe differences in their aspect, colour and
In many cases, the seeds fall at the base of the parent plant and the future
generation finds little space for growth. To avoid this problem, many plants
have developed different methods to disperse the seeds far away. One of the
areas in which nature has gone wildest in the invention of diverse structures
has been for the propagation of seeds. The dandelion, known also by the name of
pissy bed due to its diuretic properties, transforms its yellow inflorescences
into tufts, magnificent spheres composed of hundreds of miniscule parachutes (pappi),
each of which transports a seed. If you look at a tuft under the stereoscopic
microscope, you will note that the seeds are equipped with short upturned spines
which serve to anchor the seed to the soil and facilitate penetration. The
apple, the cherry and many other plants produce a sweet and colourful fruit
which attracts animals to feed on it. Normally, the seeds are resistant to
gastric juices and when the animal that ate the fruit defecates, the seeds are
released into the environment. In the same way that nectar is a reward for the
insects that pollinate the flowers, the fruit is a reward for the animal that
carries the seeds away from the plant. Chestnuts and acorns are dispersed by
squirrels and the acorns are often hidden in the ground where they are sometimes
forgotten. The maple, lime and numerous conifers instead produce winged seeds
that are carried away by the wind. Poplar seeds are covered with down which
allows them to be easily borne a great distance by the wind.
Figure 23 – Flower of Geranium pratense.
Figure 24 – Ovary of Geranium pratense
rent stages of maturation . Note how the pistil is
elongated and note the seeds at its base.
Figure 25 – Receding suddenly, the
laminae surrounding the style launch
5 seeds contained in as many sacs.
The plants which launch their seeds deserve a separate
chapter. Their flowers transform themselves into true and proper launch
mechanisms. This is the case of yellow sorrel (Oxalis corniculata),
plants of the genus Geranium, thale cress (Arabidopsis thaliana)
etc. There are many such plants and the devices that they have invented for
carrying out this task are extremely diverse. Geranium plants (Figure 23)
form five sacs at the base of the style each of which contains one seed (Figure
24). When mature, these sacs spring upwards, pulled by laminae that coil up
(Figure 25), and the seeds are projected a distance of several metres. The thale
cress has relatively long and cylindrical ovaries called siliqua (Figure 19).
When these siliqua are mature and especially if a passing animal brushes against
them, one of the two walls opens suddenly like a spring and shoots the seeds
over half a metre away. The research and study of seed dispersal systems is
particularly interesting and we will not be surprised to learn that collectors
exist. Analyse different flowers, follow their transformation into fruit and
study the seed dispersal methods. Do drawings and take photographs of their
structure and of their transformations.
Delicately remove a plant from the earth. Brush away a little
of the soil and wash off the rest so that the roots are well-cleaned. Cut off a
small root and observe the root hairs under the stereoscopic microscope.
Subsequently, you could make a transverse section of the tip of the root to
observe at a high magnification. With the biological microscope, observe the
transverse sections of the root (Figures 26, 27 and 28). On the exterior, you
will encounter the root hairs, extensions of the epidermal cells whose nucleus
is normally found in the hair. Attempt to identify the nucleus, if necessary
using a nuclear dye to highlight it. The epidermis is the tissue that
surrounds the root. At the centre of the section you can observe the central
vascular cylinder or stele where the vascular vessels xylem
(or wood), larger and more central, and phloem, narrower and peripheral,
pass. The stele is surrounded by the endodermis which is composed of a
single layer of cells. The endodermis regulates the passage of water and mineral
salts absorbed by the roots. Just inside the endodermis is the pericycle
tissue, a layer of cells capable of generating new roots. Between the endodermis
and the epidermis there is tissue called the cortex, composed of
parenchyma cells similar to that of leaves, but without chloroplasts. In some
monocotyledons, instead, the vascular tissues form a cylinder around the central
Figure 26 – Transverse section of a garlic
(Allium tuberosum). Note the epidermis, the
cortex and the central vascular cylinder.
Figure 27 – Detail of the central vascular
cylinder. Note the
endodermis, the pericycle tissue, the xylem and the phloem.
Figure 28 – Diagram of a root section.
The roots of a plant are often in symbiosis with the rhizome of
fungi forming mycorrhiza. In many trees, the mycorrhiza are visible as a
sheath on the outside of the root. In the herbacious plants instead the fungal
hyphae penetrate the interior of the root. In this symbiosis, the fungi
facilitate the absorbption of water and mineral salts by the plant, while the
plant provides the fungus with sugars and organic substances.
During the examination of the stems of herbacious plants and
the young twigs of trees it is also useful to make transverse and longitudinal
sections. Beginning at the outside, in a transverse section of the stem of a
dicotyledon (Figures 29, 30 and 31) you will find in concentric layers: the
cuticle, the epidermis, the cortex, the vascular cylinder (stele) and in some
cases the pith (medulla). The cuticle is a thin layer impregnated with
wax whose function is to reduce water loss. The epidermis can be composed of one
or more layers of cells. In a green stem, the cortex is formed of live
parenchyma cells. In the stele, the vascular tissues are found. The xylem
vessels are orientated towards the inside of the stem and transport unrefined
sap (water and mineral salts), whilst the phloem vessels are located towards the
outside and transport processed sap (sugars and organic substances) from the
leaves to the plant tissues.
Figure 29 – Transverse section of a
stem (Heliantus annuus), a dicotyledon.
&Figure 30 – Diagram of a section
of the young stem of a dicotyledon.
Figure 31 – Diagram of a stem section of a
dicotyledon
prior to the commencement of secondary growth.
The stems of monocotyledons are not organised in concentric
layers like those of the dicotyledons, but the vascular bundles are distributed
throughout all of the fundamental tissue (“scattered” bundles, Figure 32). The
pith generally contains reserve substances, but this can also be found
desiccated and with the cells empty. Also in this case, in order to better
identify the different parts of which the stem is composed and to understand
their function, it is a good idea to read the corresponding charter of a biology
textbook [001].
The longitudinal section of a stem is also useful for
distinguishing the xylem vessels from those of phloem. In the vascular bundles,
the xylem is located towards the inside and the phloem towards the outside. In
the angiosperms, the xylem is composed of tracheids and tracheae
(mature dead cells that can also form continuous vessels) and the phloem is
formed of sieve-tube cells associated with companion cells. In the
gymnosperms, the xylem is composed only of tracheids and the phloem only of
sieve-tube cells.
Figure 32 – Transverse section of a corn
In the monocotyledons, the vascular bundles are
dispersed throughout the tissue. (Field = 2.5 mm).
The support tissues collenchyma and sclerenchyma are also
present in plant stems. The cells of collenchyma have thickened walls at
the corners and are often located just inside the epidermis forming a continuous
cylinder or distinct stripes. These cells support the young stems as they grow.
Two types of sclerenchyma cells exist: fibres and sclereids. The
fibres are elongated cells grouped into bundles which are often associated
with vascular tissues. The sclereids are not elongated, are impregnated
with lignin and sometimes with mineral salts which gives them their hardness and
they often die when they reach maturity. These tissues are found in zones which
have completed their primary growth.
Figure 33 – Transverse section of a Papyrus stem,
Cyperus papyrus L.
(Cyperaceae). Dark background, ob 6 X. (Photo G.P. Sini).
Figure 34 – The same section under polarised light. The
sclerenchyma is bright in the photo. Ob. 6 X. (Photo G.P. Sini).
On the right in Figure 33, we see the external surface of a
stem, protected by a compact layer of sclerenchyma bundles (hardened fibrous
tissue for reinforcement). In the centre a vascular bundle with three large
xylem tracheae is visible with the phloem immediately to the right. The vascular
bundles are accompanied by reinforcing tissue (sclerenchyma, dark zones in a “C”
shape that in the image (Figure 34) are bright due to their high lignin content
which is birefractive). Polarised light can therefore be used to detect the
sclereids.
A meristem is plant tissue consisting of undifferentiated
cells in which new cells for mitosis are continually formed permitting the
growth of the plant. The term meristem derives from the Greek merízein, which
means “to divide& and recalls the process of cell division particularly active
in these tissues. There are two principal meristems, that of the shoot (Figure
35) and that of the root (Figure 36).
Figure 35 – Apical meristem of a
verticillata shoot in longitudinal section.
Figure 36 – Apical meristem of an onion
Figure 37 – Mitosis in an onion root
cell (anaphase). 400 X approx.
In the longitudinal section of the root you can see the
apical meristem located near the tip of the root, in which the intense activity
of cellular division which determines root growth takes place, and the root cap
which protects the tip. In the root tip, it is possible to observe cells in
various stages of cellular division or mitosis (Figure 37). For this purpose,
take an onion and put it rooting in a glass of water. After a few days, when the
roots are 4-5 millimetres long, cut off approximately 2 mm of the root tip
and crush it. Put this piece in methylated spirits for about three hours, then
place it on a slide and apply some nuclear dye such as 1% Toluidine blue for 1 -
2 minutes. If necessary, prolong the dying process. Wash away the excess dye and
apply a coverslip. Now you are ready to search for cells undergoing mitosis.
With a biology textbook, identify the stage of cell division of the various
cells: prophase, metaphase, anaphase, telophase (look also at internet
references [, 4007]).
This experiment can be best carried out with broadbean plants
(Vicia faba) whose roots have large chromosomes. Allow some seeds of this
plant to germinate in loose chippings or vermiculite (hydroponic culture).
The observation of transverse sections of leaf is very interesting
(Figures 38 and 39). The leaves are the principal organs in which the process of
chlorophyll photosynthesis takes place. Beginning from the upper surface of the
leaf, we encounter the cuticle, the epidermis, the palisade mesophyll, the
spongy mesophyll, the lower epidermis and the lower cuticle. The cuticle
is a thin layer impregnated with wax. The epidermis is formed of one or
more layers of cells. It is generally transparent and lacking in chloroplasts.
The palisade mesophyll is formed from one or more layers of cylindrical
cells arranged side by side. These cells are rich in chloroplasts which are
clearly visible under the microscope and carry out an intense photosynthetic
activity. The cells of the spongy mesophyll are irregular and arranged
in such a way as to leave empty spaces useful for gas circulation. These cells
are also rich in chloroplasts. Usually, chloroplasts adhere to the inner
surface of the cell wall (Figure 40, the darker object is the nucleus). The lower epidermis is thinner
than the upper epidermis. The surfaces of the leaf and in particular the lower
surface are rich in stomata (Figure 41). The stomata are small openings,
bordered by guard cells which regulate the amount of gas exchanged by the
leaf and limit its water loss. In the centre of the leaf the vascular vessels
pass and are called veins. On the undersurface of the leaf there are
sometimes chambers or stomatal crypts containing hairs.
Figure 38 – Transverse section of a leaf.
Figure 39 - Diagram of a leaf section.
Figure 40 – Chloroplasts in the leaf
a Bellis perennis. Diameter = 4 um approx.
Objective Lomo apo 65X NA=1.1 imm. in water.
The stomata are best seen when observed from above (Figure
41) and not in section. Therefore, to observe the stomata, remove a piece of
epidermis from the underside of a leaf. You will see not only the form of the
stomata and of the guard cells, but you can also observe the form of the cells
of that epidermis which often have the appearance of jigsaw pieces. In contrast
to the epidermal cells, the stomatal cells contain chloroplasts. Observe in the
photo also the nucleus (coloured red) which is also present in the guard cells.
The examination of the epidermal tissues of the plant is also
attractive since you can admire the different form of the cells. Many plants
possess special hairs on the lower surface of the leaves and on the stems which
are also interesting to observe. These hairs normally have the role of limiting
water loss, but they also have other functions. To take samples of the epidermal
tissue of a plant, use a pair of fine tweezers. Plants suitable for this type of
observation are mullein, cinquefoil, Artemisia spp., Correa spp., oleaster,
aubretia and all the plants with a velvety or hairy aspect. Some hairs have
specialised points for secreting viscous substances or for injecting irritating
substances into passersby (nettles). The sundew uses sticky hairs on the leaves
to capture insects on which it then feeds. Some fruits are covered with hooked
hairs which grasp to the fur of passing animals and so they are in this way
disseminated far away (Figure 42).
Figure 41 – Stomata and epidermal cells of
Figure 42 – Fruit of Cleavers Galium
(Rubiaceae). Note the hooks, useful for
adhering to animal fleece. (Photo G.P. Sini).
Figure 43 – Leaflet of Salvia glutinosa
(Labiatae) with glandular digestive
hairs. (Photo G.P. Sini)
The petals of the small orange flower of anagallis are
bordered with hairs which terminate in a small sphere. Hairs such as these are
also visible on the leaves and stems of many plants, such as for example young
rose or sage shoots (Figure 43). Search also for stinging hairs on nettles and
describe them.
An epidermal tissue particularly easy to find in all seasons
and which is very interesting to observe is that which covers the fleshy scales
of the onion. Usually, this tissue is formed of a single layer of cells. This
saves you from making a thin section of plant tissue, something which is rather
difficult to realise. In this preparation, you can observe the shape of the
cells, the primary cell wall, the nucleus and one or more nucleoli. If you are
not used to doing this, it is very possible that, despite all your efforts, you
will not be able to locate the nucleus of the cell. In fact, this is transparent
and colourless and therefore barely visible. To make it more visible, a nuclear
dye such as a 1% solution of Toluidine blue could come in useful. The nucleoli
are where intense production of ribosomes, organelles destined for protein
synthesis, takes place. The nucleoli appear as small discs inside the nucleus.
Garlic also lends itself to this kind of analysis.
After having observed a plant tissue, it is interesting to
compare the cells that compose a multicellular organism with the Protists, which
are unicellular. You realise that while the Protists are free to move and to go
wherever they wish, the cells of the tissues cannot do this. Not only this, but
these cells are also very simplified with respect to those of the Protists and
are transformed into specialised cells.
Figure 44 – Equipment for carrying out wet
Figure 45 – How to obtain plant tissue
sections without using a microtome.&
Equipment to carry out wet mounts of vegetable tissues,
Figure 44 from the left:
- 95 % alcohol in a hot water bain-marie (30-40°C);
- razor blade
- manual microtome,
- tweezers.
To examine plant tissues, you normally resort to sections. In
this chapter, we will speak only about the realisation of wet mounts,
that is, sections made by hand and if needed coloured and observed with the
addition of water or alcohol, but not treated with the complex procedure
necessary to realise permanent preparations.
Before beginning, procure the materials listed above. Some
hours before starting, wash some slides.
To make the sections, take a new razor blade,
expanded polystyrene foam or extruded polystyrene foam (not composed of beads).
If you have difficulty in finding the polystyrene, use the elderberry pith. Cut
the pith in half as though you were preparing a sandwich roll and place the
tissue to be sectioned in the middle. With the razor blade, cut very thin
sections, so thin as to be only one cell in width (Figure 45). As it is very difficult to
achieve this width, you will have to make many attempts to practice the
technique. Try also to obtain wedge-shaped sections so that at least in one area
they have the correct thickness. This system lends itself to tender tissues such
as leaves. Due to its greater hardness, the carrot is more suitable than the
elderberry medulla for making sections of the small stems that are often rather
hard to cut. To better hold the stems, make a &V-shaped” incision in the carrot.
Not indicated in the figure, but of great help in realising
thinner sections, is a stereoscopic microscope with which you can better
follow and if necessary correct the sectioning process. Observing the sectioning
of the samples under the stereomicroscope and with a bit of experience you will
be able to obtain sections even better than those possible with the manual
microtome.
With a manual microtome such as that shown in Figure 44, it
is possible to easily obtain sections, on condition that the blade is well
sharpened. A manual microtome is not very expensive, but it is also possible to
build one based on the principal of the differential screw for the precise
progress of the sample, or you can use an outside micrometer caliper (1/100 mm)
from which you have sawn off the fixed extremity.
Put the sections obtained on the slides, add some drops of
water and try to eliminate any air bubbles present. Despite all your efforts, it
is very likely that you will still have small air bubbles almost everywhere. To
attempt to avoid this problem, allow some drops of methylated spirits to fall on
the sections. Carry out this operation slowly to avoid contraction of the cells.
Often, it is better to dye the tissues to highlight not only the nuclei but also
to render the cells more visible. Prolonged immersion in alcohol tends to
destroy the chloroplasts.
As you know, children love playing. The experiments that follow
are no longer microscopic observations, but games that you can propose to small
children to tempt them to become interested in nature. If you approach children
in the right way, it is possible to win their attention and curiosity.
The Cardinal
As you can see from the figures below (Figures 46 and 47), with a capsule and a
bud from a poppy flower it is possible to create a cardinal.
Figure 46 - Poppy.
Figure 47 – How to make a cardinal out of
some poppies.
&Something well impressed on the
The poppy offers us another little game. This involves pressing a mature capsule
on the forehead to leave an impression in the form of sunrays which remains for
a few minutes.The bladder campion goes pop!
Do you remember that flask-shaped flower that you collected in such a way as to
prevent the air from escaping and which you then squashed on the back of your
hand or on the forehead of a friend to hear &pop&? This is another Silene:
Silene vulgaris, commonly known as the bladder campion. Play this game
with a child and you will see how happy they are. This plant is also used as an
ingredient in various dishes, for example &tagliatelle with bladder campion”.
Flower chains
Knotting some daisies together, you can make a daisy chain. You can also
alternate different flowers. Twist some grass or make it into a plait, then fold
it over and join the two ends. You will have a support into which you can insert
many flowers to make a garland or a crown of flowers.
The subjects to study more in depth are:
The plants (Phanerogams) and their development (the plant cell, the tissues, the
structure of the leaves, roots, stems, vascular tissues, meristems and the
growth of the plant); the production of the princip the
life cycle of the Gymnosperms and A reproduction of flowering plants
(the flower, fertilisation, the ovule, the embryo, the seed, the fruit, seed
dispersal); photosynth the energy pr
the principal families of the Phanerogams and their characteristics. In the high
school biology textbook indicated in [001] these subjects take up little more
than a hundred pages.
As a guide to the observation of plant tissues and to recognise the structures
that you will encounter, an anatomical plant atlas that contains photographs
taken with the microscope will be very useful to you: [401] and [402]. Read also
the accompanying explanations.
Botanical atlases based on drawings are also precious for the great quantity of
explanatory diagrams they contain [003] and [004]. Of particular interest for
the subject dealt with in this article are the tables which regard the plant
cell, the structure of the stem and root, the various types of leaf, flower,
fruit and seed of the superior plants.
For the identification of the different plants, you can refer to specific guides
which contain photographs and/or drawings of the entire plant and its parts,
such as flowers and fruit [404]. With guides such as these, you can manage to
identify the genus and sometimes even the species of plant.
To continue further, you can refer to an university coursebook such as the
following: [407], [410], or more recent.
The Phanerogams possess numerous specialised tissues and organs which are well
adapted to terrestrial life. The variety of solutions adopted by different
species to confront the problems of survival and competition with other species
makes the study of these vegetable organisms particularly fascinating and complex. With
the microscope, it is possible to carry out an infinite number of observations
with the immense field composed of the Phanerogams. The indications offered here
serve only as a first introduction to these plants. As you observe organs and
tissues, you will find yourself faced with unknown structures, the
identification and comprehension of which will require more in-depth knowledge.
Kingsley R. Stern - James Bidlack
- Shelley J Introductory Plant B McGraw Hill Higher E
pag 593; 2008.
Gerlach D., Lieder J.;
Taschenatlas zur Pflanzenanatomie; The microscopic structure of vascular
plants. An atlas rich of d pag 150.
Nature lower's library
field guide &The Reader's D London 1981;
Atlas to identify the herbaceous plants, provided with a lot of drawings and
AAVV; Nature lower's library
field guide to wild flowers; The Reader's D London 1981; pag. 448.
atlas to identify the woody plants, complete with many drawings and
Strasburger E.; Strasburger's Text-Book of Botany; 895 pag., Longman
Group United K
A college textbook complete with many drawings.
Ruzin, S.; Plant Microtechnique and
Microscopy; Oxford University Press Inc, USA 1999, 57 figs, 334 pag.
A superb modern reference book, full of practical information, well written
and designed, but of limited use to the amateur microscopist.
White J.; Pollen, its Collection and Preparation for the Microscope; Northern Biological Supplies Ltd.;
Look also at the works and Internet references of general character indicated in
the presentation article of this guide.
&Onion root tips
Mitosis in root tips
Floral Images
& Flore en ligne
& Sience and Plants for
Methods in Plant Histology
& Botanical Links
Botanical Microtechnique Part 1
Microtechnique Part 2
4016 - ? Pollen Atlas
Internet keywords:
college textbook botany, reference book botany, atlas botany, botanical microtechnique, botanical histology.