The nonvascular plants lack the specialized water and food conducting tissues, xylem and phloem, and do not possess the well-defined roots, stems, and leaves of the higher groups. All of the land plants are distinguished from the ancestral green algae by having multicellular reproductive organs with a sterile jacket of cells surrounding the gametes or spores, and by the development of an embryo sporophyte from the zygote, while still within the protecting jacket of the parent archegonium, the female sex organ. Male sex organs are called antheridia, as in the lower plants.

Assignment A. There are three Phyla (Divisions): Bryophyta (Mosses), Hepatophyta (Liverworts), and the Anthocerophyta (Hornworts).The gametophyte generation is dominant, with the sporophyte attached and dependent, at least for water and minerals, but often also for food, on the longer lived gametophyte.

1. Marchantia. (Class Hepaticopsida) If available, examine living plants of this or another common liverwort. There are separate male and female plants in Marchantia, but not in all bryophytes. At this time of year sexual organs will be absent, but an asexual reproductive structure, the gemmae cup, may be present. This cup is borne on the upper surface of the thallus, and holds small masses of vegetative tissue (gemmae) which can grow into new plants.(Fig. 27.8) The sexual organs, while quite different in appearance from those of mosses, are functionally very similar. The moss life cycle is investigated below.

2. Anthoceros (Class Anthocerotopsida) The hornwort, Anthoceros, differs from the liverworts primarily in the form and structure of its sporophyte, a stalklike or hornlike green sporangium that grows in length by means of a basal meristem. If available, look at living material.

3. Polytrichum, or another genus (Class Muscopsida). Examine living or frozen specimens of a moss. Using prepared slides of archegonia, antheridia, sporophytes, and protonemata, follow the life cycle diagram of a moss (Figure 27.7). Examine one or more fresh moss sporophytes. Each sporophyte consists of a foot, a seta or stalk and a capsule or sporangium. The foot attaches the sporophyte to the gametophyte and is usually too well buried to be readily discerned. The seta connects the foot to the sporangium which will produce spores at maturity. The sporangium is covered by a cap called the calyptra which can be easily removed. The calyptra is a remnant of the archegonium, and is therefore gametophytic tissue (haploid) and not really part of the sporophyte. With the calyptra removed, examine the opening of the sporangium. There is a lid (operculum) that covers one or two rows of teeth (peristomes). These teeth open and close in response to changes in humidity thereby releasing the spores.

Assignment B. Early Vascular Plants. Does it seem strange that a plant with no roots and leaves such as Cooksonia (Figure 27.10) would have a vascular system? Clearly other organs must have functioned to absorb water and minerals and to photosynthesize. An example of a plant that has no roots nor leaves yet has a vascular system may be found living today in the subtropical parts of Florida. This plant, Psilotum (whisk fern), has a green stem that is photosynthetic and has an underground stem or rhiszome that absorbs water. Look at the demonstration showing a cross-section of a Psilotum stem. The central star-shaped region of red cells is the xylem through which water and minerals are transported upward to the photosynthetic stem. Surrounding the xylem is phloem. Phloem carries photosynthates down to the rhizome. External to the phloem is a large region of thin-walled cells called the cortex. These cells function both as support and as food storage. The outside of the stem is covered by a waxy coating called the cuticle. The cuticle is crucial in preventing too much water from leaving the living cells, but it also prevents gases from entering and leaving the cells. Numerous openings in the cuticle exist and are characterized by a small pore surrounded by two cells called guard cells. Each pore and its associated guard cells is called a stoma. The plural of stoma is stomata. Stomata provide a way for the plant to obtain CO2 from the atmosphere without becoming desiccated. When the two guard cells that surround the tiny pore contain sufficient water pressure the pores remain open.

Once an efficient mechanism for retarding water loss had evolved, plants developed more specialized absorbing organs (roots) and photosythetic organs (leaves). As you examine representatives of different plant Divisions, look for other adaptations to a terrestrial habitat.

The seedless vascular plants, or lower vascular plants, are a small but diverse group of the most primitive vascular plants and their immediate descendants. The living (or extant) species are all small herbs, usually with small leaves and sporangia arranged into visible strobili. Three hundred million years ago, before dinosaurs had evolved, great forests of ferns and fern allies grew. At that time there were large woody species, some of which looked much like a huge version of the present day horse-tails. Remains of these forests are mined today, not for their fossils, interesting in themselves, but for their energy content. The next time you use electricity that has been generated by a coal-fired power plant, remember that it was the ancestors of the fern allies that we will examine today that converted the sun's energy into chemical energy long ago.

The ferns are also an ancient group, but one that is very successful and is still actively speciating. They are well known to the lay person, in contrast to the lower vascular plants. Most ferns have small photosynthetic gametophytes and large sporophytes that have conspicuous leaves borne on underground stems, except for the tree ferns of the tropics.

Assignment A. Examine living and pressed specimens of the three divisions of lower vascular plants.

1. Division Psilophyta. Psilotum (Figure 27.11), or whisk fern, is one of two living genera in this Division. Study the habit of this plant noting the dichotomous branching, the scale-like microphylls, and the tri-lobed sporangia. Spores of Psilotum are of one type (homosporous) and therefore the gametophytes produce both male and female gametes. These gametophytes are not photosynthetic and therefore rely on an outside source of energy (they are heterotrophic). This energy is supplied by a fungus. Sporophytes of Psilotum, and many other lower vascular plants, are also associated with a fungus (usually a Zygomycota). It has been suggested that this association was crucial to the exploitation of a terrestrial habitat.

2. Division Lycophyta. All three of the major living genera of the Lycophyta can be found in the Pacific Northwest.

a. Lycopodium (Figure 27.12). Using living plants and pressed specimens, observe the habit and general structure. Note that some species lack discrete reproductive regions on the stem (strobili) with the sporangia found associated with the ordinary leaves, while other species have well-defined strobili. Like Psilotum, Lycopodium is homosporous. Examine a demonstration slide showing a longitudinal section of a strobilus.

b. Selaginella. Examine pressed specimens, and if available, live specimens. Most species of Selaginella are tropical and require moist environments. An extreme exception to this generalization is the so-called resurrection plant, found in deserts of the southwest U.S. Look at a dry and a "resurrected" plant and read the explanatory material. Examine a demonstration showing a cleared strobilus of Selaginella. Notice that two distinct types of spores are present. Heterospory! What does this tell you about the gametophytes of Selaginella?

3. Division Sphenophyta (Horsetails and Souring Rushes). This group is nearly as old as the Lycophyta, it also reaches its peak in the Carboniferous period, but was probably not as prominent in the flora of that time, although fossils are common. There is only one living genus, Equisetum (Figure 27.13), that has two distinctive body forms, the much-branched horsetail, with usually separate and non-green shoots that bear the strobili, and the nearly unbranched scouring rush. In both forms the leaves are vestigial, that is, reduced to brown scales that do not carry on photosynthesis. Ancient types, however, had well formed leaves that arose from small lateral branches. For this reason they should be classified as of the megaphyll type, but because of their uniformly reduced condition, textbooks do often list them as microphylls, ignoring the evidence regarding their origin from branches. All living species and most of the extinct ones are homosporous, but a few heterosporous species occurred during the Carboniferous and Permian periods.

a. Using living and pressed specimens, study species of both the horsetail and scouring rush types. Notice the roughness of the exterior of the stem caused by siliceous deposits in the cells of the epidermis.

b. Equisetum spores. Equisetum spores have two small processes on the wall known as elaters. The elaters respond to changes in humidity by expanding and contracting, thus aiding in spore dispersal. If available, look at some of these spores which have been attached with double-sided tape to the bottom plate on a dissecting microscope. Breathe spores and watch the elaters contract.

4. Division Pterophyta (Ferns). While the ferns were prominant already in the Carboniferous, they probably reached their peak later, or possibly have not yet arrived at that point. In any case they are extremely diverse and actively evolving today, although there are many genera considered as remains of ancient orders and families of ferns. Most ferns that we study are homosporous, with well defined independent gametophytes often seen on flower pots in the greenhouse, but there are five genera, in two orders that are heterosporous, with reduced gametophytes that resemble those of Selaginella. There are several orders, many families, a large number of genera, and perhaps 10,000 species of ferns.

a. Examine living specimens of ferns collected locally. Identify the underground stem, or rhizome, and the megaphylls or fronds that are attached. Many leaves are divided into smaller segments (pinnae) which may themselves be divided into smaller segments (pinnules). Look for clusters of sporangia (sori) on the bottom of fertile pinnae. Some may be covered by a delicate piece of tissue (indusium). Place a sorus under a dissecting microscope and check it from time to time to see how the sporangia discharge the spores. Remind yourself of the fern life cycle, then examine gametophytes with archegonia and antheridia present. Be able to draw this life cycle (Figure 27.14).

b. If time permits, find 2 or 3 partners to help estimate the number of spores produced in a single year by one fern plant. First count the number of spores in one sporangium. Then count the number of sporangia in one sorus. Then count the number of sori on one pinna, and number of pinnae per frond. Finally count the number of fronds per plant and then multiply all these numbers. In a steady-state population of ferns, what is the probability that one spore will grow into a gametophyte that will produce a sporophyte? (Hint: fifty years is not an unreasonable lifetime for many ferns).

c. Examine specimens of other types of ferns including the heterosporous water ferns, Marsilea, and Salvinia, or Axolla. Pour some water over the Salvinia in an attempt to wet the surface. The hairs on the upper surface of the leaves are responsible for the ability to shed water. Why would this be important to the fern?

The seed plants fall into two principal groups, the gymnosperms or "naked-seed" plants and the angiosperms or flowering plants. The gymnosperms are divided into four Divisions: the Cycadophyta, the Ginkgophyta, the Coniferophyta, and Gnetophyta. We will concentrate on the Coniferophyta.

The seed habit involves a condensation of life cycle in a heterosporous plant, in which the megasporangium has an outer protective covering, the integument, which matures into the protective seed coat, and within which develops the megagametophyte, or female gametophyte, within which develops the embryo sporophyte of the next generation. In order for this system to function, a mechanism is needed to bring the sperm into the interior of the ovule, the immature seed, so that the egg may be fertilized. This mechanism is known as pollination. The pollen grain is an immature microgametophyte (male gametophyte), so reduced that it consists of only a small number of cells, with two functional sperm. In the more primitive gymnosperms, the cycads and Ginkgo, the sperm retain their flagella and are able to swim to the egg. In the conifers and gnetophytes, however, the sperm lack flagella and are carried passively through a pollen tube, an outgrowth of one of the cells of the microgametophyte.

In most gymnosperms there are two kinds of cones or strobili, the pollen cone or microsporangiate strobilus, commonly known as a microstrobilus, and the seed cone or megasporangiate strobilus, commonly known as a megastrobilus. Other heterosporous plants such as Selaginella have both megasporangia and microsporangia formed in the same strobilus, which is also the most common arrangement in the angiosperms.

In the conifers, the microsporangiate strobilus consists of a simple axis that bears microsporophylls, each with two or more microsporangia. The megasporangiate strobilus, however, is more complex, having been reduced from a compound or branched strobilus in which each lateral element is the equivalent of a simple strobilus. Each of these lateral elements has been reduced from the original axis and megasporophylls to a consolidated scale-like structure, the ovuliferous scale or seed cone scale. Since in the ancestral complex condition, the lateral elements were found in the axils of bracts formed on the main axis, these bracts may still be seen in the seed cones of certain conifers, such as the Douglas-fir.

The embryo of seed plants begins its existence as a parasite on a nutritive tissue within the seed, which in the gymnosperms is the vegetative tissue of the female gametophyte. The food stored in this gametophyte comes from the parent sporophyte; the gametophyte is never independent. After a seed germinates, the new leaves that are formed soon produce sufficient food so that the sporophyte plant becomes independent. This is also true of embryos of homosporous vascular plants such as ferns, although seeds are lacking. In seeds, the embryos become dormant and can remain so for long periods of time, until the seed comes to rest in a favorable place for germination, absorbs water, and the embryo is reactivated.

Assignment A. Gymnosperm diversity. 1. Ginkgophyta. Ginkgo (Maidenhair Tree). Only one genus and species of this ancient group of gymnosperms survives, and it is doubtful that any wild plants remain. It has been cultivated for thousands of years in China, but fossils of Ginkgo species are found in Oregon and Washington. It does not have seed cones, but produces naked seeds alone or in pairs on stalks that grow on dwarf shoots. The plants are dioecious, that is the microsporangiate and megasporangiate structures are on separate plants. There is a real sex difference in the chromosomes in Ginkgo. The tree is deciduous. The sperm have flagella. Examine mature female ovules, if available. The odor associated with the ripening of these ovules is strong and unfortunately close to that of rancid butter (or worse). For this reason, male trees are preferred as ornamentals although it takes many years for trees to reach a reproductive age. Ginkgo seeds are highly nutritious and are used as food in China and Japan. Several Ginkgo trees have been planted on the PLU campus. See if you can discover where they are. Examine the branches and look for short shoots and long shoots. Can you see why it is named Ginkgo biloba?

2. Gnetophyta. There are three obscure genera grouped in this Division, but probably not very closely related. Only Ephedra occurs in the new world, where it is a desert shrub with reduced, non-functional leaves and small flower-like cones. This dioecious plant is the source of the drug, ephedrine, used to treat asthma. Ephedra was also used by the Mormons, in Utah, (who wouldn't drink tea or coffee because they contain caffeine) to produce a drink that is known as Mormon tea.

3. Coniferophyta. The most dominant and conspicuous gymnosperms of the modern world belong in this Division. Many, such as firs, pines, cedars, and redwoods are of great economic importance as sources of lumber or wool pulp. Conifers are found world-wide and are generally grouped into seven families. Four of these are found in the western U.S.; the other three are from the southern hemisphere. Examine samples of a genus of each of these four families.

a. Pinus (Pinaceae). Examine a twig noting the fasicles or short shoots, borne in the axils of minute brown scale leaves that are formed on the long shoots. Each fascile is a reduced short shoot that forms a number of scale leaves, then one whorl of 1-5 needle leaves, depending on the species. No further leaves are formed but the fascicle lives for several years. The basal sheath of scale leaves persists in some species, but is soon shed in others.

b. Thuja (Cupressaceae). Western red cedar is a representative of the "false cedars", cypresses, and junipers in which the leaves are reduced to awl-shaped or scale-like forms.

c. Taxus (Taxaceae). Yews differ from the other conifers in that their seeds are borne in fleshy structures called arils, rather than in cones or strobili. Yew wood is strong yet flexible and so makes good handles and bows.

Assignment B. Life cycle of Pinus(Figure 27.17). Use your text to review the life cycle of a pine. Pine cones take two full years to mature since nearly a year elapses between pollination and fertilization. In most conifers the cones mature in a single year. So why do we use Pinus as an example? Because most textbooks do (probably because it is so widely available). Except for the extra year, however, its life cycle is very similar to that of the rest of the conifers.

1. Pollen cones of most conifers produce pollen in the spring and then wither and fall off of the tree. Pollen cones of Cedrus (the true cedar in the Pinaceae) are produced in the fall and so are available now for you to inspect. These are much larger than the pollen cones of Pinus and are borne singly on the branches rather than in clusters, but their internal anatomy is roughly the same.

Obtain a prepared slide showing a longitudinal section of a Pinus pollen cone. Examine it under the low and medium power of the microscope to get a general idea of its structure. Identify the central axis, the microsporophylls, and the microsporangia. Now examine it under high power and study the pollen grains. Each bears two gas bladders that may aid in dispersal by the winds. Locate a grain sectioned properly to show the large tube cell, the smaller generative cell, and the remains of the two disorganized prothallial (vegetative) cells.

2. Seed cones of Pinus. Examine seed cones of three ages: those that will be pollinated in the spring, those pollinated a year ago (almost), and those pollinated two years ago, now ready to shed their seeds. The wing of the seed slows the fall of the seed, allowing it to be blown further away from the parent tree. Examine a prepared slide showing a longitudinal section through a female cone. Identify the cone axis, the seed scales, and the place where the female gametophyte is developing.

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