Liverworts and Mosses Lab

LIVERWORTS AND MOSSES

The survey of the plant kingdom proper begins here with non-vascular plants - they may have conducting tissue but they lack xylem and phloem found in the higher plants. Also they have no roots but may be anchored to the ground by filamentous rhizoids.
In each of these plants the leafy part of the plant is haploid and is called the gametophyte. This is because it gives rise to male gametes and female gametes sometimes on the same plant and sometimes on separate plants. The gametes fuse to give rise to a diploid stage, the sporophyte. Meiosis occurs in the sporophyte so that the spores are again haploid. The spores germinate to produce new, haploid gametophytes.
The male gametes occur in large numbers in antheridia and when these open the gametes use their flagella to swim to the solitary female gametes which are in archegonia.
We will encounter this "alternation of generations" all the way through to the flowering plants and it is important to understand the idea, if not all the details.
All of these plants today will dry out quickly once detached from their growing medium. Examine them quickly or keep them in a little water if you must keep them for a while.
Division hepatophyta: liverworts
Collect a piece of the liverwort, strip away any medium adhering to the underside and examine both surfaces under the dissecting scope.
This is a thalloid liverwort - what does "thalloid" mean, does it have leaves?
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Does this plant have roots? What structures are on the undersurface?
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What are the most conspicuous structures on the upper surface?
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Do they remind you of stomata, how are they different?
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Have you seen this plant in the wild? What would you say it requires in its environment?
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Division bryophyta: mosses
Start by looking at the prepared slides of archegonia and antheridia of Mnium under low power on the compound microscope. You will find these structures enclosed in tiny leaves at the tips of the plant.
Which one of these look like a long, thin bottle?
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Some of the bottles contain a single cell; what is this?
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So was this a male or female plant?
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Now collect a few moss plants: look for specimens with and without a calyptra. This is an outer covering of the capsule which makes it look pointed. Without the calyptra the capsule has a blunt end.
Examine the plants under the dissecting scope.
What structure seen on the slides gave rise to the calyptra?
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Each plant is really two plants, a gametophyte and a sporophyte.
Which is the one that looks like a leafy plant?
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What sex was the gametophyte?
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Does this plant have roots? What holds it down?
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After removing the calyptra what can you see at the tip of the sporangium?
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If you can remove the next layer what do you find (you will need a dissecting microscope to see it? If you break the capsule you can see the spores; what will they give rise to?
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Lastly look at the prepared slide of the sporophyte. Which structure(s), which you could not see on your plant can you now see?
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Do you see any way this plant could control its release of spores so that they come out under conditions suitable for germination?
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Fern spores and prothallus Examine a prepared slide of the fern prothallium (or prothallus). This is a plant but not what we expect a fern to look like. So what generation or stage is this?
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What plant which you have seen today does it (somewhat) resemble? _________________
What does it have to hold it to the ground?
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Can you find any structures like those you saw on the prepared slides of moss? What are they and which is most conspicuous?
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Fern sporangia
Take a leaflet with sori from the fern provided and look at them under the dissecting scope. Does this fern have an indusium?
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The sporangia of this fern are typical of the family, Polypodiaceae which includes most of the cultivated species. You can get a better view by detaching a sorus; use a needle to push it away from the leaf and put it on a slide. Do not add water but hold it down with a cover slip and look at it under the compound microscope. You will probably see dehisced and intact sporangia and scattered spores. You may even see sporangia dehiscing if you let the specimen dry out for a while.
Try to explain the process of spore release in terms of cellular changes:
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