Like the gymnosperms, the angiosperms are adapted for life in a drier environment (although some are secondarily aquatic). Unlike gymnosperms, the seeds of the angiosperms form within an ovary on the adult plant: fruit is a ripened/mature ovary.
Monocot and Dicot Sprouts
Division
Angiospermae
is sometimes called Division Anthophyta (anthe = flower;
phyto = plant) because the common name for this group is the
“flowering plants.” Angiosperms are so named because the seeds are enclosed
within a fruit of some sort.
Division Angiospermae contains two main classes: Class Monocotyledones (the “monocots”) and Class Dicotyledones (the “dicots”). These two classes can be distinguished in a number of ways (summarized, here, but more information is included in the table, below). The seeds of the Monocotyledoneae (mono = one) contain one cotyledon (one nutrient-storage area — think of a kernel of corn), while those of the Dicotyledoneae (di = two) contain two cotyledons (think of the two “halves” of a bean or peanut). There are other differences between monocots and dicots. In general, monocot leaves are parallel-veined while dicot leaves are net-veined. Monocots generally have flower parts in groups of three or multiples of three while dicots have flower parts in fours, fives, or occasionally twos (or multiples thereof). There are also differences between the two in the arrangement of the vascular bundles (xylem and phloem) in both the roots and stems.
In plants, in general, xylem carries water up from the
roots while phloem carries sugar, etc. around (down) the plant, In
general, xylem is to the top of vascular bundles within a leaf and to the
center of vascular bundles within a stem, with respect to the phloem.
Examine, draw and label, and take notes on any available materials as indicated in the protocol.
| Monocots | Dicots |
|---|---|
| Seeds | |
| Number of Cotyledons | |
| one nutrient storage area (cotyledon) | two nutrient storage areas (cotyledons) |
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The embryo (the new sporophyte plant) in the seed consists of:
The endosperm in angiosperm seeds is a result of a rather unusual fertilization. The egg produced by the female gametophyte is 1n, but it is surrounded by some other tissue (also 1n). The pollen produces two sperm nuclei. One of these fertilizes the egg, resulting in a 2n zygote. The other sperm nucleus unites with two nuclei from the tissue surrounding the egg to form a 3n endosperm. In some species of seeds, the endosperm is larger while the cotyledon(s) is/are smaller, but in other seeds, the reverse is true. | |
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| Examine a monocot seed such as the plastic mount of sprouting corn and the slide of a cross section of a Triticum (wheat) seed (wheat berry) (Carolina #B726 or B726a = 30-5120). A large part of these seeds is endosperm (endo = within, inner), which stores nutrients for the embryo. These seeds have only one cotyledon up against the endosperm with a hypocotyl ending in a radicle and a rather well-developed epicotyl. | Examine the seeds of a dicot such as the plastic mount of a sprouting bean seed. Note the two cotyledons (cotyl = cup, socket, cavity) used to store food for the embryo plant, as well as the hypocotyl (hypo = under, beneath), terminating in the radicle (radix = root) which will become the roots. The mound of tissue between the cotyledons is called the epicotyl (epi = upon, over, beside) and will become the stem and leaves. |
| Roots | |
|---|---|
| Roots are generally underground and serve to absorb water and nutrients. | |
| Number and Arrangement of Roots | |
| many fibrous roots (think of pulling up a clump of grass) |
one main taproot (may have smaller roots branching off) (think of a carrot) |
| Arrangement of Root Vascular Bundles | |
| alternating bundles of xylem and phloem | xylem forms an “X” in center with phloem between its arms |
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Examine the slide with cross sections of a dicot (Ranunculus –
buttercup) root and a monocot (Smilax – greenbrier) root (Carolina
#B518c = 30-1892). Also, view the giant root models. |
|
| In the monocot root notice the different arrangement of the vascular tissue within the endodermis. The xylem and phloem cells alternate around the edges of the central vascular area. | In the dicot root, the xylem (xylo = wood) forms a cross or X in the center with the phloem (phloeo = the bark of a tree) in between its arms. This vascular bundle is surrounded by a layer of cells called the endodermis (endo = within, inner; derm = skin). The outermost layer of cells is the epidermis, and the region between the endodermis and epidermis is the cortex made of parenchyma cells (paren = parent, chym = juice, flavor) which are used to store food. |
| Stems | |
|---|---|
|
Stems come in various types such as:
Stems of flowering plants can be herbaceous or woody. | |
| Arrangement of Stem Vascular Bundles | |
| bundles scattered throughout the stem | bundles arranged in a ring |
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| closer view — “monkey faces” | closer view |
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| Examine a cross section of the stem of a monocot such as Triticum (wheat) (Carolina #B573 = 30-3368). In the monocot stem, most of the space within the epidermis is filled with parenchyma (pith) cells. The vascular bundles are scattered throughout this area. Within a vascular bundle, note the larger xylem cells, the smaller phloem cells to the outside of the xylem and the large intercellular passage or air space to the inside. Due to the two large xylem cells and one very large intercellular passage, the vascular bundles resemble “monkey faces.” | Examine a cross section of the stem of a dicot such as Medicago (alfalfa) (Carolina #B586). The center of the dicot stem should contain pith or parenchyma cells, around which are arranged bundles of xylem and phloem. The xylem is in the inner half of each bundle and the phloem is in the outer half. Outside of the phloem is a layer of cortex cells and beyond that the epidermis. |
| If time allows, also study samples from woody stems and bamboo to note how they grow each year. | |
| Leaves | |
|---|---|
| Leaves can be many shapes from round to heart-shaped to oblong. Leaves can be either simple or compound in form and can be either alternate, opposite, or whorled in their arrangement. Leaves which are entire, all in one piece, are called simple leaves, while those divided into multiple leaflets are called compound leaves. Compound leaves with their leaflets arranged like a feather are said to be pinnately compound (pinna = wing, feather) while leaves with their leaflets arranged like a person’s fingers are said to be palmately compound. Leaves that arise from the branch/stem in pairs are referred to as opposite leaves, while those which alternate sides up the stem are referred to as alternate leaves, and if more than two leaves arise from the same spot, those leaves are said to be whorled. | |
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| alternate, simple leaves → |  |
| alternate, compound leaves → |  |
| opposite, simple leaves → |  |
| Leaf Vein Direction | |
| parallel veins | net or branching veins |
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| microscopic cross section | microscopic cross section |
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| closer view | closer view |
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| Examine a cross section of a leaf of yucca, a monocot (Carolina #B666). In the monocot leaf, notice that all the vascular bundles are visible in cross section because the leaf is parallel-veined. | Examine a cross section of a leaf of pear, a dicot (Carolina #B669 or B669a). In the dicot leaf, you may see sections of veins cut at various angles because the leaf is net-veined. |
|
Note that both have upper and lower epidermis, a spongy
mesophyll (meso = middle, phyll = leaf) with a layer
of palisade cells along the upper portion, stomates
(stoma = mouth) which are found especially in the lower epidermis,
and vascular bundles. In general, xylem is found in the
“top and center” of vascular bundles. Note that both have a large
vascular bundle in the midrib of the leaf. Also, examine the giant leaf model. |
|
| Fruits | |
|---|---|
| Fruit is a ripened (mature) ovary (in which seeds develop/are found) and which serves as protection and means of dispersal for the seeds. | |
| Types of Fruit | |
Various types of fruits include:
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As time and samples allow, examine and draw the
structure of and/or taste various fruits such as blueberries, cherries,
strawberries, pineapple, coconut, green pepper, corn, squash, peanuts,
etc. It was mentioned, above, that dicots typically have flower parts in sets of 4 or 5, and since fruit is a ripened or mature ovary, it would be logical to expect that, in flowers that have parts in sets of five, there would also “sets of five” visible in the fruits of those flowers. Examine an apple and/or starfruit cut in half crosswise to observe the five chambers of the ovaries. |
| Flowers | |
|---|---|
| Names and Placement of Flower Parts | |
Flowers are the reproductive structures of an angiosperm and consist of four whorls of modified leaves (from outside in):
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| Examine the giant flower model and locate the outer layer of sepals, the petals within them, then the stamens, and in the center, the pistil(s). | |
| Botanists group species of plants (or, from the other direction, the monocots and dicots can be subdivided) based on a number of characteristics. Botanists pay particular attention to how the flowers are put together: | |
A complete flower has all four layers of parts.
An incomplete flower lacks one or more layers. These knotweed
flowers lack petals (corolla).
A perfect flower had both “sexes” — both stamens and pistil(s). A
monoecious
plant has perfect flowers or has both male and female flowers on the
same plant (for example, Easter lily, pea, dandelion, and rose).
An imperfect flower is lacking either the pistil or stamens. A
dioecious
plant has imperfect flowers on separate male and female plants (for
example, marijuana, hops, persimmon, and boxelder). Note that plants
such as ginkgo, a gymnosperm which doesn’t produce flowers but which
has separate male and female reproductive structures on separate male
and female plants, are also referred to as being dioecious.
A regular flower is radially symmetrical.
An irregular flower has bilateral symmetry, and is also known as a
zygomorphic
flower.
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| Number of Flower Parts | |
| flower parts in 3s or multiples of 3s | flower parts in 2s, 4s, or 5s |
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| Arrangement of Flowers on the Plant | |
Multiple flowers
can be arranged or clustered in various ways, including: 
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Observe, as available, monocot and dicot flowers. Notice that monocots have flower parts in sets of three while dicots have flower parts in sets of four or five. Dissect and illustrate a dandelion head and some other wildflower as follows.
Here is a
review of
Dandelion Flower Parts.
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| Angiosperm Life Cycle | |
|---|---|
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Angiosperms have alternation of generations with the 2n sporophyte being the dominant generation. The anthers, which are the microsporangia, produce microspores by meiosis, and the microspores develop into male gametophytes (= pollen).
The ovaries, which are the megasporangia, produce megaspores which grow into female gametophytes, each of which then produces an egg.
Note that technically the “sex organs” of a plant aren’t because they produce spores (micro- or mega-) which turn into male or female gametophytes. The gametophytes bear the true sex organs, such as they are, and are where eggs or sperm are actually produced.
Honey Bee Pollinator
Butterfly Pollinator
By some means (wind or an animal pollinator), the
pollen is transferred to the stigma of the pistil, and a pollen tube grows
down into the ovary. Eventually, two sperm nuclei travel down the pollen
tube. Pollination is the transfer of the male gametophyte (pollen)
to the stigma of the female, while fertilization (which occurs
after pollination is when the sperm nucleus and egg nucleus unite.
Angiosperms have an unusual method called double fertilization. When the sperm nuclei reach the female gametophyte, as might be expected, one sperm nucleus and the egg cell’s nucleus unite to form the new 2n zygote (which grows into an embryo sporophyte, the start of the new 2n sporophyte generation). Interestingly, however, the other sperm nucleus and two nuclei in the “center” of the female gametophyte join to form 3n endosperm tissue. In many seeds, this 3n endosperm serves as a nutrient storage area (food for the embryo).
In general, monocots tend to store food in their endosperms, and nutrients are transferred to the cotyledon only as needed. In contrast, many (not all) dicots tend to store food in their cotyledons with the endosperm being reduced to a papery coating around the embryo.
Angiosperm seeds, then, are composed of the new 2n sporophyte (epicotyl, cotyledon(s), and hypocotyl) surrounded by or next to 3n endosperm, and covered by some kind of seed coat made from the old 1n female gametophyte. The “old” 2n ovary, itself, typically grows into some kind of structure that aids in dispersal of the seeds. A ripened or mature ovary is called fruit, and can be anything from the apples and oranges that we think of as “fruit” to squash to peanut shells to maple “helicopters” to dandelion “fluff.”
| Family example(s) |
Tree or Herb? | Type of Leaves | Type of Flowers | Fruit and/or Seeds | Other |
|---|---|---|---|---|---|
| Gymnosperms | |||||
| Pinaceae
Genus Pinus pines |
tree | needles* | pine cone* (not a fruit) |
||
| Angiosperms | |||||
| Dicots | |||||
| Ranunculaceae
buttercups |
herb | 5 petals* many stamens ovary above |
|||
| Cruciferae
mustard, etc. |
herb | 4 petals* 6 stamens |
(olive fam. has 4 pet. & 2 stamens) | ||
| Aceraceae
Genus Acer maple (boxelder) |
tree | most simple opposite* |
seed with a wing | ||
| Rosaceae
rose cherry bramble apple |
both | alternate simple or compound |
5 petals* many stamens ovary under |
rose hips raspberry strawberry |
|
| Leguminosae
pea bean locust tree |
both | compound alternate |
petals joined so pea flower | peapod shaped fruit* | |
| Fagaceae
Genus Quercus oaks |
tree | simple alternate |
acorn* | ||
| Umbelliferae
carrot dill Queen Anne’s lace |
herb | many flowers arranged in an umbel* | seeds like dill or caraway | ||
| Labiatae
mints |
herb | simple opposite |
some petals joined so irregular | stems are square* | |
| Compositae
daisy goldenrod dandelion |
herb | many flowers arranged in one head* | |||
| Monocots | |||||
| Gramineae
grasses |
herb | blades w/ parallel veins | seeds like wheat or corn | ||
Some Related Links:
Other Things to Include in Your Notebook
Make sure you have all of the following in your lab notebook: