Biology Friday, January 21, 2005. Post by Sweetwind
[Sweetwind] In your webpage you mention using fractal analysis
in your research. How does this apply to botany? The only connection I can
recall hearing of is an essay of rickyjames’ called
Fern – Fractal Fusion Frustration…
but his point was that, compelling as it looks, fractals couldn’t apply in this case!
[to which rickyjames added, "I would be MOST interested in your comments on my
fern / fractal confusion..."]
[Ross] Attempts to split a fractal into smaller pieces results in the resolution
of more structure, and this is different from what we see with the more user-friendly
Euclidean mathematics of simplification. Moreover, fractal objects and processes are
said to be “self-similar”, in which the structure observed at one scale is similar to that
at another (be that scale spatial or temporal). Ferns are a beautiful example of the fractal
nature of biology: a fern leaf (frond) looks like the whole fern plant, and one leaflet
of a fern frond looks like the whole fern frond, etc. But I wholeheartedly agree with
rj’s notion that the fern does not necessarily develop by a fractal process, as this
would involve “n” starting points of fractal origin, not the one starting point!
(i.e., the rhizome, or if sexual, the spore).
In apparent contrast, I have used fractal mathematics to study plant development.
However, I have not used the algorithms to map gene expression or the development of a
germ unit into adult. Instead, I have used a fractal approach (previously only used in
ecology to study “clumpiness”) to measure and predict the condensation of chromosomal
material in certain cells of the developing female dwarf mistletoe flower, and came
up with a predictor for cell division. In ecology, the probability-density function
has been used to measure the spatial clumpiness of plants distributed in a defined
region of space, with the function being applied to digital binary images of landscapes
or generated map plots. A function that calculates a relatively higher value of the
fractal dimension (D) implies that the objects are more dispersed in 2-dimensional
space i.e., very “fractal” and self-similar, whereas a lower “D” suggests that the
objects are aggregated/clumped i.e., less “fractal”, less self-similar.
I simply took digital images of nuclei, made them binary, and used the same algorithm
to calculate the “D” values of populations of nuclei at different stages of development.
This allowed me to determine if the chromosomal material in a given population of nuclei
was truly “clumping up” and preparing to enter cell division, or was more dispersed
and not yet ready to divide. This quantitative method was more sensitive than the
qualitative “eyeball method” commonly used as a predictor. Now, I haven’t published
this anywhere (was even going to try for Nature!), so don’t steal it from me!
Oh, ok — go ahead — I’ll come up with something else!
2. Harvesting specimens
[Sweetwind] Hi Cindy, I wish you could tell us about how you go about
getting the samples of dwarf mistletoe. Do you climb trees yourself? It sounds like
you have to keep going back throughout the germination period (a year and a half!).
Do you need to get specimens from throughout the tree, or it it OK to just take the
low-hanging fruit (as it were)? The
link above splits the three in thirds from the top down to rate the infestation –
does the placement on the tree have any significance (top vs. middle vs. bottom),
or is it just a way to roughly quantify the total amount of mistletoe?
[Ross] To collect the mistletoe, which I did bi-weekly over three years,
I took little vials of preservative (glutaraldehyde) into my various field sites,
and plucked mistletoe shoots off of the infected trees. I have an (unusual?)
appreciation for statistics, so I made sure to consistently sample the same (tagged)
trees. I also consistently sampled at my eye level. However, while consistently
sampling at eye level allowed me to be very confident about developmental changes
in the mistletoe over time, I was obviously ignoring the within-tree variation of
height effects. As for the “DMT infection-rating system” you speak of, yes, it is
basically just a way to quantify infection (as you suggest). However, I would indeed
like to examine how or if mistletoe development differs at different locations on a tree.
Perhaps this is something I can subject a future grad student to: “Go climb that tree, you!”
Actually, nice extendible pruners are available for this type of elevated sampling,
although this method will be somewhat destructive, as one cannot merely pluck off
mistletoe shoots but would instead have to harvest host branches with shoots.
By sampling bi-weekly, I was able to obtain a suite of specimens at different
stages of development, and by sampling over three years, I was able to account for
some of the year-to year variation (although admittedly three years does not represent
a great degree of seasonal replication, but three years is better than two!). Where
is that grad student? Get back out there! And yes, I did sample over the winter,
as both the dwarf mistletoe and its host conifer are evergreen (I actually found
that there was a buildup of phenolic materials over the winter — antifreeze??).
I was alone most of the time during my sampling, and became a good little snowshoe-er!
Being a biologist is fun!
3. “Firehose” seed dispersal systems
[Sweetwind] In the
in discussing the way the dwarf mistletoe ejects its seeds, you say “This extreme
buildup of water pressure as a seed dispersal system is rare in the plant world.”
What other plants besides dwarf mistletoe use this method? I’d never heard of it
[Ross] Of all of the plants that eject their seeds (or other dispersal units)
explosively, the dwarf mistletoes reign supreme regarding ejection distance, being able
to shoot their seeds as far as 20 metres (165 feet) away from the source.
However, as you suspected, there are other plants that have explosive discharge mechanisms.
Irreversible turgor movements, in which water flows into the cell’s cytoplasm (aka “cellular
insides”) until the point of no return, causes the catapult action of the fruits of all
Impatiens species; the fruits “fling” their seeds away. Irreversible turgor also
causes the squirting discharge of the aptly-named “squirting cucumber” (Ecballium elaterium).
(I could make some outrageous sexual innuendo here, but I am a nice girl).
The cucumber only shoots its seeds a piddly 10 metres. Irreversible turgor movements
also allow stamens of some species (e.g., Pellionia daveauana) to fling their pollen.
In other plants, moisture absorption by the cell wall (as opposed to the cell cytoplasm)
causes opening and closing of some seed capsules, peristome movements of mosses, and carpel
twisting in many legumes (most notably Caragana). I have determined that the changes in the
cell wall composition of a special layer of cells called viscin cells in the dwarf mistletoes
leads to the explosive seed discharge.
Finally, cohesive-tension dehydration, which is essentially the reverse of cell wall
moisture absorption, can also occur in the cell walls, leading to discharge. The best
example for this is the opening mechanism of a fern’s sporangium and dehiscence of the spores.
4. A Corny Question
[rickyjames] Cindy, until you came along to take her place, my
female botanist heroine over the years has been
ever since I read an article about her years ago in
and I’m wondering if you are familiar with
her work on corn.
Who were the role models that got you interested in a career in botany?
[Ross] Wow — firstly, thank you for the compliment. I am indeed familiar with
Dr. Eubank’s work, and am thrilled to be considered alongside her. She has faced much
adversity in her personal and professional life, and has endured with grace and style.
I wish I could give you my vote for what I think the true ancestor(s) of modern corn is
(are) (Teosinte, a different graminoid, or some undiscovered progenitor), but I think patience
with the genetic analysis is needed. I can see the problem some researchers have with
Dr. Eubank’s work (her theories almost mirror the now defunct “ontogeny recapitulates phylogeny”
concepts). But the right genetic test of the right highly-conserved genetic markers with the
right computer algorithm should at least be able to eliminate some contenders. Go, Mary!
I also like the way she decided to make some $$ from her results; no one could argue that the
plants she bred had great agricultural features!
As for my “botanical heroes/heroines”, I have to say that the first botanist to really
“twig” my interest would be Gregor Mendel, the Father of Genetics. Wow — what a smart, smart guy.
We should start a debate — Mendel vs. Einstein. (Or maybe not…). In my opinion, Mendel
is also the father of modern scientific investigation. I am not a geneticist per say, BUT his
work got me so interested in genetics and probabilities that I actually insist on teaching
Genetics! I also really like the brain workings of that F.W. Went fellow: he performed the
early extremely elegant experiments on phototropism (bending of plants toward the light),
and realized that the bending response was due to a chemical signal (an auxin). Of course,
the great Katherine Esau, plant anatomist and microscopist extraordinaire, is an inspiration
to me as a plant anatomist, botanist, and woman. Her recent passing was a great loss.
Now, as you might be able to discern from my ramblings, I am a bit of a generalist, with
interests in many areas! The person who got me to focus on botany was also the person
who taught me first-year biology, and subsequently became my Ph.D. advisor,
Dr. Michael J. Sumner. I think he is even more enthusiastic about plants and teaching
about them than I am. And he is a really, really nice person too — we remain good friends today
(this, as you may or may not realize, is NOT common regarding Ph.D. students and their advisors!).
5. Fav Flower
[rickyjames] Is mistletoe really your favorite, or something else? Somehow I just can’t imagine that a
self-professed plant gynecologist wouldn’t be interested in
most associated with
sex on so many levels
scandal to boot. Are you?
[Ross] As far as plants go, the mistletoes are really quite something, being parasitic, evergreen,
having such unusual mechanisms of reproduction including the explosive discharge, having such folklore
and history attached to them, and also having unusually chemistry (compounds isolated from European
mistletoe have been used in anti-cancer therapy!). But it’s not really a looker, is it? I must confess,
though, that I am not a big fan of orchids, either; I think they are actually kind of ugly (the ones that
look like flies, not necessarily the ones that look like “other things” — don’t want to insult myself!),
although they are of course biologically fascinating, particularly regarding their “intimate” association
I must admit that I still fall into to the “what a girl” stereotype — I really like pretty flowers.
My favourite flowers are tulips. Like roses, they stand alone in a bouquet (fiercely independent!),
but are of course more unusual than roses, and a lot tougher! Some of you might be recalling an old
schoolyard joke involving roses and pianos, etc., but you just leave it outside!
6. I like this question
[barakn] I was going to ask a similar one, except that I was going
to mention my favorite parasitic plant genus, the paintbrushes. These grow in
B.C. and are sexual tricksters, considering that the colorful part most of us
would call a flower isn’t a flower. What is it about dwarf mistletoe that
makes it so fascinating to study?
[Ross] I like the paintbrushes, too. They are holoparasites “whole parasites”,
completely lacking chlorophyll, and taking all useful substances — water, minerals, and sugars –
from their hosts. Mistletoes, on the other hand, are considered hemiparasites “half parasites”;
they still take water and minerals from their hosts, but they are green (i.e., have chlorophyll)
and are thus able to make their own sugar by photosynthesis. The dwarf mistletoes, while still
considered hemiparasites (as they are green), also take some sugars from their host.
So physiologically, these plants are intriguing. As an anatomist, I am particularly interested
in the cells and development within the dwarf mistletoes, but another area I intend to explore
is the interface between the dwarf mistletoe’s “root” (really a haustorium — an absorptive structure)
and the host bark. I want to know how the cells of the parasite and host interconnect.
for the paper on the pollen tubes refers to the plant’s placenta. I have never heard that term used
for parts of anything but mammals. Is it really a similar structure? Is it found in many plants?
[Ross] The main female organ of all flowering plants is the flower’s pistil, which consists
of the sticky stigma (pollen receptor), style (elevates the stigma), and ovary at the base (contains
one or more ovules). The word “ovary” simply means “vessel” in Latin. The placenta (Latin for “table”)
is merely the thickened portion of the inner ovary wall to which a plant’s ovule(s) is (are) attached.
Yes, this is true for (essentially) every flowering plant! And yes, the flowering plant’s placenta
and ovary are truly analogous to a mammal’s! Moreover, both the plant and mammalian placenta will
function as a transfer organ for materials to pass from old generation to new. However, following
pollination and fertilization in the flowering plants, the ovule will become the seed and the ovary
will become the fruit (not so for mammals!) And the flowering plant placenta isn’t quite so gross
as the mammal’s. (Ah, you are starting to see why I didn’t go into medicine!). Non-flowering seed
plants (like conifers including the pines and spruces aka the “gymnosperms”) do not have ovaries or
placentas. Their ovules are “naked” (the Latin “gymno”) on cones, not protected in any vessel.
8. Effects of domestication
[apsmith] I’m afraid I’m not at all familiar with plant biology,
but I’ve just been reading Jared Diamond’s
“Guns, Germs and Steel”,
and he makes quite a big deal about the variety of ways in which domestication of
plants by humans has resulted in many different kinds of obvious and not-so-obvious
changes in their biology. Selection for larger sizes, seedlessness, or larger seeds
when the seed is what we’re after; self-pollination, quick germination, etc. etc.
Can you comment on reproductive differences between wild and domesticated species
you’ve looked at, or any general comments on that subject?
[Ross] The artificial selection you speak of has taken place over centuries,
leading to the many varieties of plants we have today, and is really form of adaptive biological evolution,
depending on three components of variation, selection, and reproduction. Advances therefore involve
one or more of these components. Sometimes selection was made consciously, with unconscious results
occurring. For example, while selecting for large seeds, sometimes we may have unintentionally also
selected for disease susceptibility! Moreover, with artificial selection, there is always a concern
that there is too much inbreeding (lack of variation) in the crop; if one plant is susceptible to a
disease, due to their genetic uniformity, all will be susceptible.
Nonetheless, I know of a few more useful differences between domesticated and wild species,
additional to the ones you’ve mentioned: domesticated peas with non-bursting pods, grains with
non-shattering heads, and seeds of various species that have lost germination inhibition (so that
germination not only happens quickly but all at once). Note how in each case, should the plant ever
escape to the wild, it would not likely succeed, due to the loss of some key feature of its reproduction.
Genetic modification is, to a certain extent, artificial selection done really, really quickly.
Therefore, it is highly unlikely that genetically modified organisms could “escape” to the environment
and cause damage, as they would essentially be puppies in a wolf world. They are not tough monsters,
they are wimpy wimps. This is not to say I agree with genetic modification, as, quite frankly,
these scientists aren’t just always simply changing genes, they are often adding genes (and usually
very randomly to the genome!). I am going to reserve judgment on this until more evidence one way or
the other emerges.
As far as European Christmas mistletoe goes, there are domesticated mistletoe “farms” in Europe,
but to my knowledge, no one has compared the fruits (or other aspects) of these mistletoes with their
wild cousins. This is particularly interesting, considering that this mistletoe requires a bird vector
for seed dispersal. Time for me to do some research overseas! Thanks, apsmith! And while no one
in their right mind has domesticated the highly pathogenic dwarf mistletoe, there has certainly
been domestication of its host(s) on tree farms; some of these farms had to be abandoned due to
dwarf mistletoe infection. Intriguing…
9. Fire And Rain In B.C. Forests
[rickyjames] In early December I drove up from Seattle and spent
the day in Vancouver with janra, my first real trip to Canada.
We went for a short hike in the forest and I was VERY impressed
with just how beautiful it was. I hadn’t realized the forest in
that part of the Northwest was actually considered a “rain forest”.
Anyway, you’ve got a wonderful corner of the world in which to study botany.
One of the most curious things we saw (to me, anyway) were a half-dozen
or so burned trees. These were BIG charred hollow trunks going up to 10 or 15
meters above the ground with no “insides” and no real damage to speak of on
any of the nearby trees or ground. There weren’t, from what I could see,
any limbs from the trees on the ground, either. I’ve spent a LOT of time
in hardwood forests in the South, and I’ve NEVER seen anything like that
a single time before, much less a half dozen times in walking distance.
They strongly reminded me of so called
I saw in Hawaii many years ago, but of course that’s not what formed them.
Janra said lightning caused them, but I still find that a little hard to believe.
In the South I’ve seen lots of lightning strikes on trees, and while they do cause
fires and generally tear up the side of the tree, down here they never just burn
out the core of the tree. Have you ever seen charred trees in B. C.?
Your comments? [to which janra added: "I said I guessed that it was lightning.
I don't know for certain. Just for a bit more detail, the burned-out stumps were much
bigger in girth than anything around them. That park was logged about 100 years ago,
so I'd imagine they are remnants from before the logging. (Which would explain the
lack of branches...)"]
[Ross] Thank you for favourably commenting on my new home in British Columbia!
Unfortunately, I am not situated in the coastal rainforest zone, but rather in a very arid
region of the interior, which I have on occasion perhaps rather harshly called the “desert
in the middle of the oasis”. But I digress — I really love my new corner of the world.
So as you might guess, I am quite new to B.C. (August 2004, actually), and have not seen
the trees you speak of, and am, if you pardon me, a little “stumped” on this one!
But being someone who likes to sit around thinking, I have some ideas! Maybe one
(or more) is actually right…
Firstly, I agree that these trees represent old growth from a few centuries ago, due to
their large size. Their “branchless-ness” might be a result of logging, but COULD merely
be due to the fact that many old trees lose their bottom branches (why maintain branches
at the tree bottom when the light will just be blocked out by the branches higher up?).
In addition, I know that the highly suberized nature of a tree’s bark, particularly
the thick bark of large rainforest trees, makes the bark highly resistant to heat, especially
compared to a tree’s inner wood. Thus, should lightning hit the top of a tree, the lightning
could potentially ground itself through the tree, causing damage within, but not harming
the enveloping bark. But why more than one tree?? Hmm hmm…it’s hard to believe lighting
struck several trees top down. Perhaps, instead, lighting caused crown fire, and the fire
then traveled down the more susceptible inner wood, leaving the resistant bark alone.
The bark could even act as a chimney, allowing ignition to occur rapidly and completely
throughout the tree’s inside, channeling heat upwards and leaving the bark unaffected.
Hey — that sounds pretty good! Or…perhaps alternatively some sort of heart-rot fungus
specific to wood attacked the tree’s insides. Darn — I’d have to see the trees after all.
Time for a trip to the coast!
[rickyjames] The cool thing about mistletoe is its ability
to be green all year without being a conifer. From an evolutionary standpoint,
why haven’t all green leafy plants adopted the mistletoe route and stay
green year-round? It seems to me that dropping leaves is much more common.
Which came first – falling leaves or mistletoe?
[Ross] Firstly, it is generally believed that the non-flowering seed plants (gymnosperms/conifers)
evolved before the flowering plants. Also, as you said, most conifers are evergreen, whereas most flowering
plants are deciduous (leaf-droppers). Thus, the evergreen habit evolved before the deciduous habit.
Also as you noted, mistletoes are unusual, being flowering plants as well as evergreen; as the flower came
late in evolutionary history, the mistletoe’s adoption of an evergreen lifestyle had to come late as well.
And naturally, the parasite had to evolve after the host.
But why? Well, forget about mistletoes for now, and think about evergreen conifers (picture a pine
tree with needle leaves) and deciduous flowering plants (picture an oak tree with broad leaves); one can
think of advantages and disadvantages to each lifestyle. By keeping leaves on year-round, there is no lag
period in the spring in which a conifer has to take the time to develop/put out leaves – time that would
waste precious summer sunlight. However, as a disadvantage, the conifer has to be designed so that rare
warm winter days do not cause premature water movement through the plant: a conifer trying to draw water
from the frozen ground would be hurting itself! (Sometimes they do this anyway. The browning of conifers
in the wintertime is due to prolonged warm winter sun exposure and dehydration). So, the leaves of a
conifer are designed to minimize water loss at any time of the year, particularly during the winter.
A deciduous tree, on the other hand, might have to take the extra time to put out leaves during the spring,
but never risks being dehydrated in the winter (there are NO LEAVES for which water to be deleteriously
drawn up through the plant during the odd warm day in winter). Thus, the deciduous plant can afford to
have nice broad leaves in the summer; yes, there will be a lag period for leafing out, and yes there will
be substantial water loss in the summer, but the photosynthetic gain will outweigh the water loss.
As an end result, deciduous trees are the better photosynthetic competitors at the warmer temperatures,
relegating the coniferous has-beens to colder locations. Interestingly, though, the deciduous plants
lose their competitive advantage at the colder temperatures, because the growing season is shorter, and
the time it would take the deciduous plant to put out leaves in the delayed spring would just cost too
many sunlight hours.
A mistletoe, be it the European mistletoe growing on a deciduous plant host, or a dwarf mistletoe growing
on a conifer, can afford to be evergreen, as its host will take care of the winter dehydration problem
in the appropriate mechanism (no leaves or needle leaves, respectively). So the mistletoe will be able
to start photosynthesis right away in the spring (even the lazy dwarf mistletoe, which will do some of its
own photosynthesis but then begin to rely on the host’s photosynthesis).
11. Wells Gray Park
[Sweetwind] Hi Cindy, your web page says you are director of the
Friends of Wells Gray Park.
I take it
provincial parks are run by the province,
so do you have to deal with provincial officials? Or more with the membership
of the Friends? How long have you been doing it, and what does it entail?
[Ross] You would like to think that the provincial parks are cared for by the province,
wouldn’t you? But the British Columbia (B.C.) government has been a little lacking in park maintenance,
cutting funding and services. Members and directors with the “Friends” try to find funding sources to
help keep essential park services running. We also try to hire students to put on interpretive programs
during the summer, and also advertise and fund various family day-type outings. We also have a membership
section dedicated to preserving and advertising the park’s very interesting history. In addition, we
try to keep abreast of park “developments” that have the potential to harm the park. For example, there
is a group wanting to put up a parking lot. While parking means more visitors and interest (generally,
a good thing, if kept in check), we are concerned that the parking lot is the stepping stone for the
“Wells Gray Park Shopping Mall and Amusement Centre”. I am exaggerating a bit, but you see my point.
We have conservation and nature at the heart of our organization.
We do indeed deal with the province, but as I have only been a director since October 2004,
I haven’t gotten into any “discussions” with government officials yet. I am instead in charge of the
newsletter, which I had better get to work on …like…now…
I really appreciated the opportunity to express myself here. Thank you for the excellent questions.
SciScoop Science is owned and operated by David Bradley Science Writer.