Coniferophyta

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Coniferophyta

• Pine Life Cycle

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Headwaters of the Mississippi River
Boreal Forest and North to Taiga Conifers
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Taiga also exists at high altitude leading to the
timber lineeven a lower latitudes.
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Conifer stems start as eustele, with bicolateral
bundles, and endarch xylem maturation. They
become woody with annual growth rings in 2 xylem
and periderm replacing epidermis.
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Root exarch, diarch, becoming woody
Name the layers!
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Leaves are needles in fasicles (short shoots)
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Needle cross section Name the layers
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Conifers produce cones! (Microsporangiate and
Megasporangiate) Monoecious!
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These pink cones are microsporangiate fir strobili
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Microsporangiate cones of red cedar (Arbor vitae)
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Longitudinal section of a microsporangiate
strobilus. There is a cone axis with
microsporophylls. Each have two microsporangia
containing microsporocytes. Microsporocytes
undergo meiosis to produce microspores. Microspore
s undergo mitosis to make an endosporic
microgametophyte. The pollen grain is shed to the
wind.
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This view shows a close up of six
microsporophylls. What is contained in the
microsporoangia at the time of the preparation
are probably microsporocytes or immature
microspores. The mature microspore wall would
have ear-like bladders to improve movement in
wind.
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Similarly, this longisection also has
microsporangia that appear to have solid tissue
(pink) inside. Again, this tissue is either
microsporocyte or very immature microspores.
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These are microspores for sure. How can you tell?
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The microsporangiate cones open up and start
shedding what?
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Pollen grains How can you tell?
Tube cell Generative cell Prothallial cells (2)
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The number of pollen grains shed in Spring 1 is
vast!
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Once the pollen is shed, the microsporophylls dry
up and the microsporangiate cone usually is shed
and falls to the ground. Here they are drying up
as the new needles are being formed.
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Crater lake in Oregon the floating stuff is
pollen!
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In spring, the number of cones shedding can be
vast too!
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The target of the pollen is the megasporangiate
cone. Here is the female cone of tamarack
(larch). The pink cone scales are the
megasporophylls with two ovules each. The
gray/green extending leaves are bracts. Each
bract-megasporophyll unit is a compound cone
scale.
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The megasporangiate cone of pine in Spring 1
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In pine, the megasporophyll and subtending bract
are fused and joined to the cone axis as a
unit. There are spaces between the scales for
pollen infiltration. The ovules are on the upper
epidermis with micropyle facing the cone
axis. Pollination droplets pick up the pollen
grains that infiltrate deeply enough.
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After pollination in Spring 1, the
megasporophylls begin to thicken and close up the
spaces between the cone scales. Syngamy will not
happen for quite some time later!
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Spring 1 the pollen is in the micropyle, but the
megasporocyte has not even undergone meiosis yet!
Prom night!
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The tube cell starts to grow to the nucellus to
digest a path into the (someday) megagametophyte
with its egg. The generative cell has not made
two sperm yet.
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Meiosis is happeningas the tube cell is
digesting the nucellus
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Four haploid products of meiosis in megasporangium
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The ,megagametophyte is rapidly growing through
Summer 1
Free-nuclear in the middle with large
vacuole Cellularized near nucellus (M-sporangium)
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By Fall 1 the egg is in an archegonium. Name the
layers.
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Getting ready for syngamyin Spring II. The
pollen tube has digested partway through the
nucellus. The egg in the archegonium has lots of
storage reserves. Syngamy occurs in Spring II.
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There are two nuclei in this huge cell. Which is
which? What part of syngamy has occurred already?
What has not?
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Here that later step in syngamy is just happening!
Tardy sperm arrivals have no chance!
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Here is metaphase of which division of what
process to make what? Notice it is free-nuclear!
Early summer II.
The first zygote generally make the embryothe
tardy egg is toast.
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At the end of that division, here are four what?
Of what? Ploidy?
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When cytokinesis does occur, it is asymmetric.
The larger cells are suspensors, the smaller
cells are potential embryos.
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Three of probably four potential embryos on at
lest two suspensors.
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Four competing embryos on suspensorsthe best
wins!
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Successful embryo develops on its suspensor. Name
the rest of the layers
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Mature seed longisection. Micropyle to right.
Name everything.
Does a pine embryo have one or two cotyledons?
Fall II
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Pine embryo wm OK, this is easier to count for
sure!
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Identify the various cones here and what is
happening in each.
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Identify the various cones here and what is
happening in each. What is the season for each of
the cones? The reproductive steps occupy two
growing seasons in many pines. This is obviously
one of those species!
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Identify the cone and the season if this is a
two-year pine!
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This conifer is probably a one-season
species. How can you tell?
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This is a megasporangiate cone of Douglas fir.
Name the parts.
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Ditto What is happening at this time?
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Are these cones or berries of Juniperis?