Experiments in plant diversity
Janice M. Glime
jmglime at MTU.EDU
Sun Feb 28 13:33:59 EST 1999
> I am in the process of developing labs for a course on (green) plant
> diversity. The course will be taught in an evolutionary framework. I would
> like to demonstrate both commonality and variation in function and relate
> these to morphology and anatomy. What I have in mind are simple
> physiological experiments to show that there is, indeed, a connection
> between structure and function in organisms other than angiosperms.
My students love the lab where we put water on dry mosses like Hedwigia
and Tortula and they watch the leaves unfold. It is interesting to
compare mosses like Sphagnum, which has primarily external conduction,
with Polytrichum, which has primarily internal conduction. Have students
put the base of these mosses in test tubes with a small amount of dye in
them. They can compare the rate at which the dye moves up the plant and
then take cross sections to see where most of the dye is. In Sphagnum it
will enter the stem from the outside and reach the center of the stem
last. In Polytrichum, it should be in the middle first (I haven't tried
it to see, but Polytrichum has primarily internal conduction and uses
hydroids, which are readily visible in cross section). The rate of
movement can easily be compared to the rate in celery or carnation or
Dispersal is a good thing for comparison. Get a moss with good, easily
seen teeth in the capsule and hydrate the area around it. The teeth will
respond to changes in atmospheric moisture. Don't wet the teeth
themselves, but a drop of water on the leafy portion of that moss and its
neighbors can send the seta into gyrations and cause the teeth to flex.
Dicranella heteromalla is good for this demonstration. Preserved strobili
of Equisetum will work if you wash the preservative off them, then squash
some sporangia and watch the spores and elaters as they dry. To speed up
the drying, remove the strobili from their wash and let them dry, then
apply alcohol to the extracted spores. Ferns will also perform by flexing
their annuli. They require a technique similar to that of the Equisetum.
If you use fresh fern sporangia, the sporangia need to be mature.
Branching patterns and apical dominance should be interesting to
compare, at least with mosses and monocots vs dicots. I think the others
would be either too slow or too seasonal. Snapdragons work well. I
haven't tried this on many mosses, but Fontinalis can be used, but will
take several weeks to respond. This might be a good one for a field trip -
look for plants of all sorts, including club mosses, mosses, and
horsetails (but not Equisetum arvense) to see evidence of sub-apical buds
developing branches when the tip is damaged. If a field trip is not
feasible, perhaps you can collect evidence or take pictures to show it.
Tropisms work well in mosses and flowers. I suspect they will work with
the other groups too, but I haven't tried or observed them; these are a
fast response - 1-2 days.
I would expect epidermal peels of lycopods to be difficult or
impossible, but I haven't tried. I wonder if one could see enough in a
whole mount of something like Selaginella kraussiana. The guard cells are
small in these.
Sun and shade leaves should be doable in all groups, although a little
slow. I induced Fontinalis antipyretica var. gigantea to produce copious
red pigment by taping it to a piece of vertical filter paper or paper
towel that acted as a wick to the water at the bottom of a baby food jar
(tall style) and culturing this under fluorescent light. The tape was a
narrow strip about 4 mm wide. The moss actually "bled" red pigment onto
the paper towel in the area near the tape. I don't think this was a light
response, but it certainly was a stress response. Sun damage and sun
responses should be apparent in mosses, ferns, and seed plants, but I
don't know about horsetails and club mosses. I would expect Selaginella
to be more responsive than Lycopodium, and your local plant nursery could
probably give you some advice on suitable ferns.
Please send me a summary of the responses you get to this question! It
will be ideal for my new combined botany and plant morphology course.
Thanks for getting me to think about this.
Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime at mtu.edu
More information about the Plant-ed