13.3
Applying Inquiry Skills
5. A microscopic view of a plant section reveals a greater than usual
number of xylem cells. What might this suggest about the plant’s
ability to conduct and store water? In what kind of environment
would a large number of xylem cells be beneficial to survival?
Explain why.
6. Identifying and learning the names of plant tissues can be challenging, even for experienced plant biologists. Create a table
which lists the three major tissue types, the specific cell types in
each, and their special structures including the name, a description, and the function of each structure. Add a section to describe
the location and importance of meristematic tissue.
13.3
Leaves
Green leaves are the major sites of photosynthesis. They contain chlorophyll, the
green pigment necessary to capture light energy. They must also be able to obtain
carbon dioxide from the air and water to use as the building blocks for sugars
and starches, the products of photosynthesis. If maximizing photosynthesis were
the only objective, we would expect leaves to be very wide to maximize their
exposure to the light, and to have systems to readily obtain carbon dioxide and
water. However, there are other equally important considerations. Leaves must
not dry out—a difficult problem when faced with bright sunlight, hot, dry air,
and high winds. There is also the problem of hungry herbivores. As a result,
leaves occur in a great variety of shapes, sizes, and textures. Leaves also have a
variety of internal structures. These characteristics have evolved very gradually.
They are the features which allowed the plants to survive the biotic and abiotic
factors of their habitats. Those plants with characteristics which did not promote
survival simply died.
The blade is the flattened main body of the leaf. Leaves are positioned along
the stem at points called nodes. The distance between successive nodes is called
an internode (Figure 1). Typically, leaves have a network of veins or vascular bundles of conducting and supporting tissue. In many plants, each leaf is connected
abiotic: describes anything related to nonliving things. Abiotic factors include temperature, humidity, light availability, and soil
conditions such as water content, texture,
and mineral composition.
nodes: the locations where leaves are
attached to the stem
internode: the space between two successive nodes on the same stem
blade
axillary
bud
petiole
biotic: describes anything related to living
things. Biotic factors are all living things in
an area and include interactions within and
between species, such as competition and
predation.
blade
node
sheath
internode
(a)
node
node
(b)
Figure 1
Typical leaf forms of (a) dicots and (b) monocots
Plants: Form and Function 501
compound leaf: a leaf that is divided
into two or more leaflets
to the stem by a leaf stalk called a petiole. The vascular tissue in the stem usually
sends out one branch to the leaf through the petiole. Once in the leaf, the vascular
tissue branches out. If these new veins branch and rebranch throughout the whole
leaf, the leaf is said to have net venation. This is the normal pattern for dicots
(Figure 2(a)). If these new leaf veins tend to run from the petiole to the leaf tip
without joining one another, the leaf is said to have parallel venation. This is the
normal pattern for monocots (Figure 2(b)). If the leaf has a single, undivided
blade, it is called a simple leaf. A compound leaf has a blade divided into two or
more leaflets (Figure 3).
Figure 2
(a) A small part of a dicot leaf (from a silver
maple tree) showing net venation
(b) The monocot leaves of a plant called rose
twisted stalk, showing parallel venation
(a)
simple leaf: a leaf that is not divided into
leaflets
(a)
Figure 3
Examples of (a) simple leaves and (b) compound leaves
502 Chapter 13
(b)
(b)
poplar
(Populus)
red buckeye
(Aesculus)
oak
(Quercus)
black locust
(Robinia)
maple
(Acer)
honey locust
(Gleditsia)
13.3
Stomata
During photosynthesis, the leaf must acquire a constant supply of carbon dioxide
and be able to release the oxygen produced. The exchange of these gases is regulated by tiny pores called stomata (singular: stoma). Stomata are found in the epidermis of leaves or stems but are mostly found in the lower epidermis of leaves.
As well as regulating carbon dioxide and oxygen diffusion, stomata also allow
water vapour to escape from the leaf. The loss of water vapour in plants is called
transpiration. The water diffuses and evaporates into the air spaces of the leaves
and out to the atmosphere through the stomata.
When the stomata are open, the plant can obtain needed carbon dioxide;
however, the plant also loses water, which can pose significant problems for the
plant. When the stomata are closed, water is conserved, but carbon dioxide
cannot be obtained. The opening and closing of each stoma is regulated by a pair
of sausage-shaped guard cells (Figure 5).
transpiration: the loss of water through
the surfaces of the plants. Most transpiration
occurs through leaf stomata.
guard cells: the cells that occur in pairs
around each stoma in the epidermis of a leaf
or a stem. They regulate the opening and
closing of the stoma.
cuticle
upper epidermis
palisade mesophyll
xylem
vein
phloem
spongy mesophyll
lower epidermis
air spaces
cuticle
Figure 4
A three-dimensional drawing of a typical leaf
showing internal and surface structures
2 pairs of guard cells
Most epidermal cells do not contain chloroplasts. However, the guard cells
around the stomata do contain many chloroplasts. When a pair of guard cells contains low levels of water, they are somewhat limp and rest against each other,
closing the stoma. As water builds up in the leaf tissues, as it does most nights, the
guard cells tend to swell. However, the portion of the cell wall of each guard cell
that faces the other is thickened. As the cells enlarge, they swell less where their
walls are thickened. The pairs of swollen guard cells look similar to kidney beans
and the stomata are now open. At sunrise, photosynthesis begins in the chloroplasts. Carbon dioxide levels drop and oxygen levels increase in the leaves relative
to the concentration of these gases in air. Because the stomata are open, gaseous
exchange occurs by simple diffusion. Water vapour is also lost.
Throughout the day, as the water concentration in the guard cells drops, the
cells begin to shrink. Gradually, as the pairs of guard cells become limp and collapse, the stomata close. The opening and closing of the stomata are also related
to the concentration of carbon dioxide in the guard cells. This mechanism tends
to allow the stomata to be open in the daytime for gaseous exchange and closed
at night to conserve water.
During the hottest part of the day, plants may lose excessive water. If this loss
occurs, the guard cells, along with all the other cells, lose water and become limp.
The stomata close and as a result, gaseous exchange of carbon dioxide and
oxygen is prevented and photosynthesis is slowed down or temporarily stopped.
In addition, light levels, temperature, and abscisic acid concentrations play a key
role in the opening and closing of the stomata.
stoma closed
guard cells
thickened
guard cell
walls
(a)
H20
stoma open
CO2
epidermal
cells
CO2
(b)
H20
Figure 5
The closing (a) and opening (b) of stomata
are regulated by the levels of water and
carbon dioxide in the guard cells.
Plants: Form and Function 503
Try This
Activity
Counting Stomata
• Obtain a prepared slide of the epidermis of any leaf. Alternatively,
ask your teacher how to make your own wet mount, or imprint.
• Observe the specimen under medium power and note the appearance and pattern of stomata among the epidermal cells. Note the
shape of the guard cells.
• Count the number of stomata in a single field of view. If there are
too many stomata, count the number in a one-quarter “pie section”
of the field of view and then multiply your result by four.
• Your teacher will provide you with the field of view diameter for
your microscope from which you can determine the radius.
Determine the area (in square millimetres) of your field of view
using this formula: area = pr 2. Show your calculations with your
recorded result.
• Use your results to estimate the total number of stomata on a leaf.
Explain how you obtained this number.
Mesophyll
mesophyll: the region of photosynthetic
cells between the epidermal layers of leaves
palisade mesophyll: one or two layers
of brick-shaped cells, rich in chloroplasts and
found tightly packed beneath the upper epidermis of most leaves
spongy mesophyll: a layer of irregularly
shaped cells containing chloroplasts between
the palisade mesophyll and the lower epidermis of most leaves. Many air spaces are
randomly distributed within this layer.
DID YOU KNOW ?
The single most abundant protein on Earth,
RUBISCO (acronym for ribulose 1,5-bisphosphate carboxylase/oxygenase), is the enzyme
responsible for creating organic molecules
containing carbon from the inorganic carbon
dioxide in the air.
504 Chapter 13
Between the upper and lower surfaces of a leaf is a photosynthetic region called
mesophyll (Figure 4). The mesophyll consists of parenchyma cells containing
lots of chloroplasts. In most plants, the mesophyll has two different areas based
on the orientation and shape of the cells. The palisade mesophyll occurs under
the upper epidermis. Here, the cells are shaped like bricks and are tightly packed
together in one or two layers. The longer sides of the cells are at right angles to
the upper epidermis. These palisade cells contain many chloroplasts and are the
primary site for photosynthesis. The spongy mesophyll lies between the palisade
mesophyll and the lower epidermis. These cells have fewer chloroplasts, are irregular in shape, and are randomly arranged with large air spaces scattered among
them. These air spaces promote the rapid diffusion of carbon dioxide into cells
and oxygen gas out of them. In the leaves of some plants, the mesophyll does not
form two distinct areas.
As a result of photosynthesis, carbon dioxide levels drop in the mesophyll
cells. Since carbon dioxide levels are lower within the cells than in the surrounding air spaces, carbon dioxide diffuses into the mesophyll cells, providing
more reactants for photosynthesis. Similarly, as oxygen gas is produced within
the cells during photosynthesis, the concentration rises, resulting in the diffusion
of oxygen gas out of the cells into the surrounding air spaces. If the stomata are
open, gaseous exchange occurs between the air spaces and the atmosphere. If the
stomata are closed, the process of photosynthesis quickly consumes the available
carbon dioxide within the air spaces in the mesophyll and further photosynthesis
effectively stops.
Leaf Adaptations to Abiotic Factors
The extreme conditions of some terrestrial environments have made it difficult
for many plants to survive. Diversity of species has resulted in the survival of some
species in those locations but not others. In addition, diversity within a species has
also allowed those individuals of a species which could somehow cope with the
extreme conditions to survive, while others died. Plants with very broad leaves to
trap low light energy will survive in shaded areas but die if they germinate in
open, sunny fields. Plants whose leaves appear in the very early spring, before
13.3
Try This
Activity
Examining Water Loss
In this activity, you will examine water loss in leaves.
Materials: large fresh green leaf, scissors, water, two small binder clips
or clothes pins, paper towel, balance, incubator or small fan
Procedure
• Trace the leaf on the paper towel. Cut out the leaf shape.
• Wet the paper leaf until it is saturated but not dripping.
• Determine and record the masses of the leaf and the wet paper
cutout.
• If possible, place the leaf and the cutout in a drying oven or incubator overnight. Otherwise, hang them up to dry. You may wish to
use a small fan to shorten the drying time.
• When the paper cutout looks noticeably drier, determine the final
masses of both the leaf and the cutout.
• Calculate the percent loss of mass for both the leaf and the paper
cutout.
• Comment on the effectiveness of the leaf cuticle in preventing
drying out.
leaves of the surrounding trees emerge and create shaded conditions, will survive
in a deciduous forest, but plants whose leaves appear late will not survive.
Most conifers are evergreen, which means they keep their leaves throughout
the winter. This characteristic is especially beneficial in regions with a short
growing season. These trees avoid expending the large amounts of time, energy,
and nutrients required to grow a complete set of new leaves each year. The leaves
of most conifers, such as pine and spruce, are modified as thin, long needles. The
needles have a small surface area and a thick, waxy cuticle. Although these features make the leaves inefficient for photosynthesis, they greatly reduce water
loss. This prevention is advantageous since, during the winter, lost water cannot
be replaced by roots buried in frozen ground.
Plants that can survive in areas of low precipitation or high salt content in the
soil usually have leaves with thick layers of water storage tissue or are covered with
an extra thick, waxy cuticle to prevent water loss. These plants also tend to have
fewer than the usual number of stomata. The spines of cacti are the remnants of
leaves. Water loss is reduced because they have very few stomata and extremely
small surface areas. Photosynthesis takes place in the fleshy, green stems. Cacti
thrive in sunny desserts but would not survive in shaded forests (Figure 6).
(a)
(b)
Figure 6
(a) Conifer needles are modified leaves
which reduce water loss but still perform
photosynthesis.
(b) Cactus spines are more radically modified
leaves. Most photosynthesis occurs in the
fleshy stems.
Plants: Form and Function 505
Leaf Adaptations to Biotic Factors
toxin: a poison produced in the body of a
living organism. It is not harmful to the
organism itself but to other organisms.
Figure 7
Some leaf adaptations discourage hungry
herbivores. Plants such as (a) woolly lamb’s
ears, which have hairy leaves, stems, and
flower heads, and (b) common milkweed,
which have a horrible taste, are avoided by
herbivores. Look closely and you can see a
monarch butterfly caterpillar among the
leaves and seed pods of the milkweed.
Leaves are extremely vulnerable to herbivores. Herbivores are attracted to tender
leaves with mild flavours. Any plants that happen to have tough, hairy, prickly, or
bitter leaves are more likely to survive herbivore appetites (Figure 7). However,
there is always a tradeoff. The very characteristics which help the plants survive
herbivores reduce their photosynthetic efficiency. Also, diversity among the herbivores has allowed certain herbivores to cope with the plant features. Some herbivores have tough mouth tissues, efficient teeth, or special digestive enzymes;
others have a poor sense of taste.
Diversity also means that while some plants continue to supply nutritious
food for herbivores, other plants produce toxic chemicals in their tissues which
actually control herbivore populations. The nicotine in tobacco leaves is an insecticide. An even more convoluted situation involves the common milkweed plant
and the monarch butterfly. While milkweeds produce a toxin which has a horrible
taste and is highly toxic to almost all insects and large herbivores, monarch butterfly caterpillars are immune to this poison. In fact, the milkweed toxins accumulate in the fatty tissues of these caterpillars. In this way, the caterpillars and
adult monarchs are themselves toxic and unpalatable to their enemies.
(a)
(b)
Other Leaf Adaptations
In addition to performing photosynthesis, some plants use leaves to accomplish
a number of other functions (Figure 8). In some plants, all the leaves are modified, but in others, regular leaves exist along with modified ones. Onion bulbs are
modified leaves that are specialized for storage of water and nutrients. Some
plants develop specialized leaves called tendrils for attachment to surfaces or
objects for support. A variety of plants, such as cacti, produce sharp spines,
which are actually modified leaves. Plants with such specialized leaves survive
better than those without them when dealing with hungry herbivores. Even the
petals of flowers are modified leaves which attract pollinators for reproductive
purposes. The Venus fly-trap, the pitcher plant, and sundews are all examples of
carnivorous plants, although the term carnivorous is misleading because they do
not require animals as food; they all can photosynthesize. However, studies have
shown that they thrive when animal protein is available. There are also some
506 Chapter 13
13.3
(a)
(b)
(c)
(d)
(e)
(f)
plants which have lost not only their leaves but also their ability to photosynthesize. For example, Indian pipe leaves are reduced to tiny bits of tissue. There are
no chloroplasts in any part of this plant. Thus, these plants are heterotrophic.
They are saprophytes and obtain their nutrients from decaying organic material
in the soil. Indian pipe has vascular tissue and complete flowers.
Practice
Understanding Concepts
1. State the primary function of leaves.
2. What two functions are served by vascular tissue within leaves?
3. Why are guard cells essential?
4. What two substances control the swelling or collapse of guard cells?
Figure 8
Leaf adaptations.
(a) An onion bulb consists of modified leaves.
Note the dried real leaves at one end of the
bulb and dried up roots at the other end.
(b) A very prickly plant growing along a
roadside in southern Spain
(c) Colourful petals of common spring garden
flowers
(d) Leaves of the pitcher plant attract, trap,
and digest insects in a pool of water.
(e) Leaves of sundew with sticky projections
that bend down to trap insects that land
on them
(f) Indian pipe has no chlorophyll and is a
heterotrophic plant.
5. Describe four plant features which help protect them from hungry
herbivores.
Activity 13.3.1
Leaf Adaptations
Leaves are the site of photosynthesis and exhibit many adaptations to maximize
their photosynthetic efficiency. Leaves are also the site of water loss through transpiration and evaporation. Up to 90% of the water taken in by roots is lost to the
air through leaves. Plants called xerophytes can survive, or even thrive, in waterdeficient environments and have evolved numerous features to conserve water.
In contrast, plants which live in water are called hydrophytes and exhibit features
xerophytes: plants that survive or thrive
in areas with very little moisture
hydrophytes: plants living on or in water
Plants: Form and Function 507
mesophytes: plants that thrive with
moderate moisture
uniquely suited to their environment. Most plants thrive in environments with a
moderate water supply and are referred to as mesophytes.
Questions
What are the features of a typical mesophytic leaf?
What leaf adaptations are found in xerophytes?
What special features do the leaves of hydrophytic plants have?
Materials
prepared slides of Syringa, Yucca, Zea (corn), Potamogeton, Pinus (pine),
Verbascum, and Oleander
whole samples of Aloe, rubber plant leaf, and fig leaf
microscope
any potted mesophyte, such as Geranium or Coleus
any potted xerophyte, such as jade
cobalt chloride paper
paper clip or adhesive tape
plastic wrap
Procedure
Part 1: Observing Leaf Adaptations
This lab will consist of a series of numbered lab stations. Each station will have
one or two specimens for you to examine. Take approximately 10 min to complete and record your observations at each station. Your teacher will instruct you
on how and when to change stations.
1. Copy Table 1 into your notebook but leave large spaces for your answers,
about 15 lines for each row of the table. Your whole table may occupy 3
notebook pages. Record your answers as you complete the steps. At each
lab station, use the information and questions provided here as guides to
your observations. List and describe the most significant features of each
leaf. Add drawings where appropriate.
Table 1
Station
Specimen(s)
1
Syringa
?
?
2
Yucca
?
?
Aloe
?
?
Pinus
?
?
Zea
?
?
Verbascum
?
?
3
4
Observed feature(s)
Adaptive significance
Oleander
?
?
5
Potamogeton
?
?
6
Philodendron
?
?
Station 1: Syringa—A Mesophyte
2. The prepared Syringa slide has a cross section of a leaf blade. View the leaf
under low power. This leaf represents a typical mesophyte dicot leaf.
Observe and record the shape of the whole cross section of this leaf.
508 Chapter 13
13.3
3. View the slide under medium and high powers. Look for the palisade mesophyll. Describe and draw what you see.
4. Look for the dark pairs of guard cells in the epidermal layers which open
and close the stomata. Compare the number of guard cells seen in the
upper and lower epidermal tissue.
Station 2: Yucca and Aloe—Succulent Xerophytes
5. View the prepared Yucca slide under medium power. Look for large numbers of vascular bundles and a thick cuticle.
6. Break off a small piece of one Aloe leaf. Observe and describe its interior.
Station 3: Zea and Pinus—Monocot and Gymnosperm
Xerophytes
7. View the prepared slides of a Zea leaf and a Pinus needle using medium
and high powers. Corn and pine are well adapted for conserving water
during hot summer days. Note that most stomata are located on the upper
epidermis of the corn leaf. The leaf also possesses unusually large epidermal cells. These cells collapse in hot, dry conditions, causing the leaf to
curl up and inwards. Describe the position of the pine guard cells relative
to the needle surface.
Station 4: Verbascum and Oleander—Xerophytes with Specialized
Surface Features
8. View the prepared slides of Verbascum and Oleander under medium and
high powers. Note the hairs extending from the surface of the Verbascum leaf.
9. Carefully note the location of stomata within the large pits on the lower
surface of the Oleander leaf. These pits also contain tiny hairs. Look for a
thick cuticle and multilayered epidermis in the Oleander.
Station 5: Potamogeton—A Hydrophyte
10. View the prepared slide of a leaf cross section under medium and high
powers. Note that the palisade layer is near the upper leaf surface. Note the
location of the stomata and the size of the spongy mesophyll layer. What
effect would this specialized tissue have on leaves that grow in water?
Station 6: Philodendron—A Tropical Rain Forest Vine
11. Philodendrons are vines that live in tropical rain forests. They begin life on
the ground in deep shade and grow up into the canopy along tree trunks.
Examine the leaves, stems, and aerial roots of this plant. Note the “drip tip”
on the leaf.
Part 2: Testing Transpiration in Leaves
12. Dry cobalt chloride paper is blue. In the presence of water, it turns pink.
Select a healthy, large leaf on a potted mesophyte. Do not remove this leaf.
While being careful not to damage the leaf or plant stem, fold a piece of
cobalt chloride paper over the edge of the leaf, covering part of the upper
and lower leaf surface. Cover the cobalt chloride paper with a slightly larger
piece of plastic wrap. Fasten the paper and plastic to the leaf with a paper
clip or tape, being careful not to damage the leaf (Figure 9).
13. After 15 min, remove and examine the indicator paper. Record your
observations.
14. Repeat steps 12 and 13 using a xerophyte plant.
Figure 9
Without removing or damaging the leaf,
apply the cobalt chloride paper as shown.
Plants: Form and Function 509
Analysis
(a) In the Syringa leaf, how does the location of the palisade layer enhance
photosynthesis? Where are most of the stomata located?
(b) Compare the Yucca and Aloe leaves with the leaves of other common
plants. How do the special features of these leaves contribute to their
function?
(c) What is the function of the thick cuticle of the Yucca leaf?
(d) Comment on the size and shape of the Pinus needles. How does their
overall size influence water loss?
(e) How does Zea’s ability to curl its leaves in hot weather influence
water loss?
(f) How might the hairs on the Verbascum leaf influence surface air flow?
How might the hairs influence water loss?
(g) How do the stomatal pits on the Oleander leaf influence water loss?
(h) How is the location of the stomata on the Potamogeton leaf well suited
to a floating leaf?
(i) Discuss whether the large air spaces in the Potamogeton leaf are wasted
space or if they serve a useful purpose.
(j) Describe the leaf surfaces of the Philodendron as smooth and waxy or
rough and dull. How would the surface influence what happens to
rainwater that falls on these leaves?
(k) How might the “drip tip” on Philodendron leaves influence what happens
to rainwater that falls on these leaves?
(l) What is the advantage of having leaves that shed surface water quickly?
(m) How is water able to escape from the surfaces of leaves? What structures are involved?
(n) Compare the transpiration rates from top and bottom leaf surfaces.
Account for any differences.
(o) Compare the overall transpiration rates from the mesophytes and
xerophytes. Account for any differences.
(p) What advantages are there to having stomata in the lower leaf surface
rather than the upper leaf surface?
(q) What features or structures of a xerophytic plant allow it to survive in
hot, dry environments?
(r) If the leaves of xerophytes have far fewer leaf stomata than those of
mesophytes, what can you infer about the potential rates of photosynthesis and growth in these plants? Explain your answer.
Leaves
1. Leaves are the site of photosynthesis.
2. Transpiration and evaporation of water and gaseous exchange of carbon
dioxide and oxygen occur through the stomata..
3. When there is plenty of water in the guard cells, they swell in a way that
opens the stomata, but when the water content decreases, the guard cells
collapse, closing the stomata.
4. The mesophyll is a photosynthetic layer consisting of palisade and spongy
mesophyll.
• The palisade mesophyll cells, found just under the upper epidermis
of leaves, are brick shaped, tightly packed together, and have many
chloroplasts.
510 Chapter 13
13.3
5.
6.
7.
8.
• The irregularly shaped, spongy mesophyll cells with interspersed large air
spaces lie between the palisade mesophyll and the lower epidermis of
leaves and have fewer chloroplasts.
Leaves have adaptations (e.g., cactus spines, evergreen needles, tough fibres,
hairy leaves, thorns, bright colours, and toxic compounds) to various abiotic and biotic factors.
A xerophyte is a plant that survives or thrives in areas with very little
moisture.
A hydrophyte is a plant living on or in water.
A mesophyte is a plant that thrives with moderate moisture.
Section 13.3 Questions
Understanding Concepts
1. What is the advantage of having air spaces within leaves?
2. List the features of xerophyte leaves that reduce water loss.
3. Describe a special adaptation found in each of the following
leaves:
(a) Potamogeton
(b) Pinus
(c) Verbascum
(d) Aloe
(e) Zea
4. Photosynthesis requires water and carbon dioxide and produces
sugars and oxygen. Using proper terminology, describe the pathways taken by these reactants and products as they enter and/or
exit the leaf.
5. Describe the key problem that exists for plants that have many
broad, thin leaves. How does the cuticle help overcome this
problem?
6. Tropical rain forest plants have no shortage of water.
(a) How have the leaves of rain forest plants evolved to cope
with rainy conditions?
(b) How might rain forest plants be harmed by having continuously damp or wet leaves?
7. During the winter, the ground is frozen. The days can be cold
and sunny while the air is very dry. Given these conditions, suggest reasons why pine trees have evolved to retain their leaves
during the winter. Also, suggest the benefits of their very
narrow, waxy leaves.
Applying Inquiry Skills
8. A number of leaves are obtained from a rare plant collection and
carefully examined. Based on the following information, classify
each leaf type as a mesophyte, xerophyte, or hydrophyte.
• Leaf A: broad and thin with a double palisade layer and many
stomata on the lower leaf surface
• Leaf B: no stomata on the lower surface but does have stomata
on the upper surface; vascular bundles almost completely
lacking in xylem
• Leaf C: very fleshy with many vascular bundles but very few
stomata
9. Examine a variety of houseplants. Name each one and describe
any features it has which might allow it to survive dry, humid,
cold, and hot climates. Look for and mention any plants with “drip
tips.” Speculate on the natural habitat of each plant described.
(continued)
Plants: Form and Function 511