In the plant kingdom it is interesting to observe many of the characteristics of adaptation to the environment. There are nonvascular plants such as mosses, liverworts and hornworts. There are vascular plants which can be either seedless like the whiskfern, club moss and ferns or the seed bearing plants which are either gymnosperms (non-flowering plants: conifers, cycads, Gnetales, and Ginkgo) or angiosperms, the flowering plants. In this exercise you will be looking at the Gymnosperms. These plants are found very early on in fossil records and one of their main characteristics is that their seeds are exposed to the environment, not enclosed in ovaries as with the flowering plants. There are four main divisions of gymnosperms: Cycadophyta, Ginkophyta, Gnetophyta and Coniferophyta. It is the latter, the conifers, that make up the greatest number of gymnosperms.

Using your textbook define or explain the following terms.

Megosporocyte –The embryo sac mother cell, a diploid cell in ovary of plant that undergoes meiosis, producing four haploid megaspores.

Megagametophyte (female gametophyte) – In heterosporous plants, the female gametophyte, which develops from a megaspore.

Integument - A covering, investing or coating structure or layer; coat or ovule.

Egg cell – Ovum: female gamete: egg.

Nucellus – In seed plants, the megasporangial tissue which persists around the megaspre (embryo sac) and the megagametophyte that developes within it, and eventually forms the inner layer of the ovule wall.

Micropyle – Small pore or channel in coat at apex of ovule through which the pollen tube enters; corresponding aperture is testa of seed between hilum and point of radicle

Pollen tube- Tube that develops from a pollen grain after attachment to stigma and which grows down towards ovule, entering it at the micropyle and delivering male gametes, or in some cases just male nuclei, to fuse with the female gamete.

Part 1 - Cycadophyta

Look carefully at a sample of a cycad. Look at the shape of its leaves and the radial symmetry of the plant. These plants are dioecious (separate male and female plants). However, these plants take a very long time to reproduce. If material is available, observe a male (pollen-producing) and a female (ovule/seed-producing) cone. Make a sketch of the female cone below.

Notice that the seeds are not enclosed within any type of fruit as they are in flowering plants (consider an orange or a tomato for example). These "naked seeds" are characteristic of all gymnosperms.

Cycads are also quite intriguing because their sperm have flagella and they actually swim into the egg cell!

The seeds of cycads (as well as all gymnosperms) are filled primarily with female gametophyte tissue that the embryo uses as a source of nutrients when the seed germinates. If material is available, cut a seed in half. Sketch what you see below and identify the embryo and female gametophyte tissue.

Part 2 - Ginkgophyta

Ginkgos are large trees and are also dioecious. The female is easy to recognize when the seedpods have fallen to the ground in spring. They smell of rancid butter due to the presence of butyric acid! The male plants do not smell and are the preferred type to plant. It was brought over from China and Japan as an ornamental tree, otherwise it would not exist in this part of the world. They are also fairly resistant to pollution and are thus planted in many cities nationwide.

What advantage and disadvantages are there to having a separate male and female trees?

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If material is available, observe the young Ginkgo biloba tree. The leaves have a fairly characteristic shape- they are bi-lobed. Sketch one of the leaves below.

Ginkgo, just like cycads, produces flagellated sperm cells! These two groups, however, are the only seed plants to produce flagellated sperm.

Part 3 - Coniferophyta

These are often very large trees which can get to be very old. They produce their seeds in cones (hence the name). Although there are many examples of conifers (spruce, fir, larch) we will focus on the pine tree and its cones.

Obtain a branch of a pine tree from your instructor.

Are the leaves an unusual shape? Considering that Pine trees have leaves year round, even when much water might not be available in the winter, what advantage might this leaf shape confer?

The leaves are arranged in bundles. Do all the bundles have the same number of leaves attached? What is that number?

These trees are green all the year round. Does this mean that they never drop their leaves?

Some people are allergic to pine pollen. Observe a prepared slide of pine pollen and make a sketch below. Notice the large air bladders on each side of the pollen grain. These help make the pollen airborne.

The pollen is released in large quantities, blown through the air, and hopefully lands on a female cone. Eventually, the pollen will germinate and a pollen tube will grow toward an egg cell. Sperm cells (non-flagellated) are produced within the pollen tube and are used to fertilize an egg cell found on the female cones.

Observe a prepared slide of a female cone that shows the megasporocyte (the diploid cell that is capable of undergoing meiosis and developing into the female gametophyte. Make a sketch below.

The megasporocyte undergoes meiosis to produce 4 megaspores. Three of those die, and one develops into the female gametophyte (megagametophyte).

Observe a prepared slide of a mature Pine female gametophyte. Make a sketch below. Be sure to label the relatively large egg cells.

Now observe a prepared slide of a Pine seed after fertilization has taken place. Make a sketch below. You should be able to identify the embryo that is growing through the female gametophyte tissue and using it as a source of nourishment. Can you see the remnants of the pollen tubes? Yes

Also, obtain a Pine nut and slice it longitudinally right down the center. You should again see the embryo embedded within surrounding female gametophyte tissue (remember that the next time you eat pesto or anything else that requires Pine nuts!).

Part 4 - Gnetophyta (Gnetales)

The Gnetales represent an intriguing group of plants that are the closest living relatives to flowering plants (angiosperms). In fact, although they are gymnosperms, they posses many features found in angiosperms such as vessel elements, double fertilization (no endosperm though), and broad leaves.

There are only 3 genera of Gnetales: Ephedra (also called Mormon's tea; it grows in southwestern US); Welwitschia (this plant grows only in Africa and is truly bizarre); and Gnetum (we'll focus on this plant today).

Observe the Gnetum plants available in lab. Notice that they look nothing like most other gymnosperms and could be easily mistaken for a flowering plant.

Gnetum is also dioecious, having separate male and female plants.

If a female reproductive structure is available, observe it and make a sketch below.

Notice that the ovules (immature seeds) are not enclosed within an ovary.

Now, observe the male reproductive structure.

You should see small pollen-producing structures, but do you also see ovules? yes

Would you guess that the "male" plant is capable of self pollination and fertilization? yes,

In fact, a graduate student here at UND discovered that the ovules formed on the male plant are not functional- they contain defective female gametophytes and are therefore never fertilized.

Pollen must travel to the female plant for reproduction to take place.