LABORATORY EXERCISE #10
KINGDOM FUNGI - KINGDOM PLANTAE
THE FUNGI AND PLANTS
Upon completion of this laboratory the student will:
Textbook: chapters 17 and 18
Photo Atlas: chapter 5, pp 63, 67 – 72, 74 – 76, and chapter 6, pp. 84 – 86, 95, 97 – 115
PART I – THE KINGDOM FUNGI
Although the fungi are usually studied by botanists (plant biologists), they belong to a separate kingdom. While there are some similarities between plants and fungi, there are also major differences, the most conspicuous being a lack of chlorophyll in the fungi. This means that the fungi are all heterotrophs, either parasitic or saprophytic. Saprophytes obtain energy from dead organic matter, while parasites live on or in, and at the expense of, a living host. Another major difference between plants and fungi is in the composition of the cell wall, which in most fungi is composed of chitin - as in the exoskeleton of arthropods - rather than the cellulose of plants.
The body of the fungus is termed a mycelium, and is composed of many thread-like hyphae. The mycelium is usually diffused within the substrate on which the fungus lives and is seldom seen by humans. The most conspicuous part of the fungus is usually the fruiting body, constructed of a dense network of hyphae, which assumes a rather consistent shape in many taxa. The structures termed "mushrooms" or "toad stools" are examples.
The fungi, though somewhat humble organisms, impact our lives in many ways. They ruin our clothes, rot our homes, contaminate our food supplies and infect our bodies. They are also serious plant pathogens, causing more diseases in plants than do bacteria. On the positive side, we rely on fungi to make our bread light, add a unique taste and smell to ripe cheeses and contribute a bit of a "kick" to some of our favorite beverages. We also rely on the antibiotic properties of some fungi as we manufacture important medicines. The most important divisions (phyla) of Kingdom Fungi include:
1. The largest division of Kingdom Fungi is called the sac fungi. This group includes such tasty delights as truffles and morels, as well as some of the most dangerous pathogens. The name "sac fungus" comes from the tiny sacs in which the sexual spores are produced. Diseases caused by sac fungi have devastated two of North America’s most important forest trees. Dutch elm disease has decimated the American elm, a prized shade tree, and chestnut blight has virtually eliminated the American chestnut from the forest.
2. The fungi probably familiar to most students belong to the club fungi . This includes most of the common mushrooms, including the ones commercially available in your grocer's produce section, along with the puffballs and bracket fungi. Also included are the rusts and smuts; serious agents of disease in the cereal grains. Your Photo Atlas shows the development of a typical mushroom, as well as the formation of the tiny "clubs" or basidia on which the sexual spores develop.
3. The lichens are included here for want of a better place. They do not exactly fit into our scheme of classification because they are composite organisms. A lichen is composed of a fungus - usually a sac fungus - and an alga. The arrangement seems to work well for both species, with the fungus giving the alga a moist, protected place to live, with adequate light, and the alga providing food for both through photosynthesis. While there are many interesting lichens, we can lump them into three categories:
A. The crustose lichens form a thin crust over the substrate, usually a rock or tree. These lichens look as though they have been spray-painted on!
B. The foliose lichens are leaf-like. One could easily use a fingernail to pull them from the surface on which they are growing.
C. The fruticose lichens are described as shrub-like. They are sometimes used as miniature trees or shrubs in model railroad landscapes.
PART II: THE PLANT KINGDOM
The Kingdom Plantae is generally considered to include all the multicellular, autotrophic organisms. They typically have a cell wall of cellulose and store energy in the form of starch. They also have an interesting life cycle, which consists of alternating sexual and asexual stages. Meiosis in the plants leads to the formation of spores rather than gametes.
While most of the plants with which we are familiar are terrestrial organisms, one group is overwhelmingly marine or aquatic. These are the algae. Because these plants live in the water, they have not evolved the support tissue required by land plants, nor do they need special tissues to transmit water from one part of the plant to another. Since the tissues that perform these tasks in terrestrial plants are termed vascular tissues, the algae are included with the non-vascular taxa.
The term "algae" has no technical meaning today, as we know that the three groups are not really closely related and probably represent separate branches of the evolutionary tree. We simply retain the term to mean the multicellular, non-vascular aquatic plants.
Division Bryophyta contains the plant equivalents to the amphibians. These plants are terrestrial organisms which have not been able to divorce themselves from the water. They lack vascular tissue, which means no true roots, stems or leaves, and must therefore retain a small, low-growing plant body. The bryophytes also have motile sperm, a holdover from their algal ancestors, and must have at least a thin film of water for fertilization to be affected. For the most part, then, the bryophytes are limited to moist, shady habitats.
The life cycle of the moss, a typical bryophyte, is found on page 370 of your textbook.. Note that the life cycle is divided into two parts, the gametophyte generation, which is haploid (has only one of each chromosome pair in its cells) and the sporophyte generation, which is diploid (has two of each type of chromosome). In the moss - and indeed all bryophytes - the gametophyte is the most conspicuous and dominant of the two generations. The green bed of moss that you see in the woods is a bed of moss gametophytes! This is the sexual stage of the life cycle, producing gametes in special organs termed the antheridia (male) and archegonia (female).
The fertilized egg or zygote represents the beginning of the sporophyte generation. The rather inconspicuous moss sporophyte is the asexual stage and produces, through meiosis, many haploid spores that are released in great clouds and blown by the wind to disseminate them about the countryside. These spores mark the beginning of the gametophyte generation.
There are two major groups of bryophytes, the mosses and the liverworts. We will examine the mosses as representative bryophytes.
Vascular plants include most of the plant species with which we are familiar. The plants which make up a majority of our food, the forest trees from which our dwellings are made, the plants which furnish the fibers of which our clothes are constructed, all are vascular plants. So also are the shrubs, which surround our homes, the delicate flowers that brighten our lives and the logs crackling in the fireplace. The distinguishing characteristic of this group is its possession of vascular tissue. This tissue serves the plants in much the same way as the animal circulatory system, delivering materials from one part of the plant to another.
There are three major groups of vascular plants.
Primitive Vascular Plants
These plants do not form seeds, include the ferns, club mosses and horsetails. These taxa have life cycles in which the sporophyte generation is predominant, unlike the mosses studied previously. The gametophyte generation, though diminutive, is none-the-less free living. Like the mosses, these plants reproduce by the use of spores, rather than seeds. All three groups have long fossil histories and once dominated the land. Those species existing today hang on in rather specialized ecological niches.
The gymnosperms are primitive seed plants which are present in abundance today and which are very important to modern humans. The cone-bearing trees (conifers) are a part of this group. They include the oldest, tallest and bulkiest living organisms (bristle-cone pines, redwoods and sequoias, respectively). Most of the timber used in building construction comes from such conifers as pine, fir, cedar and redwood, and we enjoy using the beautiful evergreen gymnosperms for ornamental plantings.
The sporophyte generation dominates the gymnosperm life cycle; indeed, the gametophyte has been reduced to only a few cells and there are two types, male and female, both of which usually form on the same tree. Seeds which are not formed inside a fruit also bring about reproduction. The name gymnosperm means "naked seed," a reference to the small seeds of the conifers which lie naked upon the scales of the reproductive structure or cone.
All gymnosperms are woody plants. In addition to the conifers, the cycads and ginkgos make up the group.
The angiosperms are the flowering plants. The reproductive structure of the angiosperm is the flower and the seeds are protected by the thickened wall of the ovary, within which they form and mature. This "ripened" ovary, with its seeds, is termed a fruit. The angiosperms include large forest trees with their woody supporting stems, as well as the smaller herbaceous plants which lack wood.
It is difficult to over-emphasize the importance of angiosperms in today's world. Most of the mid-latitude and tropical forests are made up almost exclusively of "hardwood" trees which belong to this group. Basically all of the plant materials we eat and/or feed to domestic animals are the products of angiosperms. Most birds, mammals and insects find home and sustenance among these plants, and we enjoy the sight and smell of their flowers and languor in their shade. Can you imagine a world without this group of plants?
The angiosperms are divided into two major groups, based on a few easily-identified characteristics. Illustrated in your Photo Atlas, these are:
A. The monocots are all herbaceous. Their flower parts are in threes or multiples of three, and a cross-section of the stem reveals scattered bundles of vascular tissue. The leaves of monocots have the vascular tissue confined to many parallel veins. Included in this group are the lilies, the orchids and the grasses.
B. The dicots may be herbaceous or woody. Their flower parts are in fours or fives or multiples of these. Their vascular bundles are arranged in a ring, and the veins of the leaves form a network. All of the hardwood trees are dicots, as are many crop plants such as beans, tomatoes, cabbage, etc., and a majority of the spring flowers.
Angiosperms may complete an entire life cycle in one year, over-wintering as seed (annual plants), or they may live for many years (perennials). Some woody angiosperms are evergreen (southern magnolia, for instance), while others are deciduous, losing all their leaves in the Fall and replacing them in Spring.