79 - = / 79 = . Name ______________________________
Pinus Life Cycle
You have observed some gymnosperm diversity last week; today you will observe the details of the life
cycle of Pinus, one of the most common conifers (Coniferophyta). This life history is similar to that of all of the
gymnosperms, although the details might vary. For example, while the life cycle of some pines is a two-year
process, in other conifers and most other gymnosperms it is a one-season process. All the gymnosperms are
heterosporous with the megasporophylls and the microsporophylls grouped together in separate cones, but most
gymnosperms are dioecious with only one type of cone (male or female but never both) on a particular individual.
Pine, however, is monoecious; the microsporangiate cones occur near the ends of branches and the megasporangiate
cones are found at the apex. Other conifers include: spruce, fir, hemlock, redwood, etc., as well as the southern
hemisphere podocarps and araucarias. It includes the largest and the oldest living individual organisms known.
•Observe branches of a few representative genera available in the laboratory. On your walks
around campus, you will see others and might make some observations as you go along. Note
that some genera, such as Juniperis, have two types of foliage leaves: longer needle-like
leaves and much smaller scale leaves. Since the needle leaves are characteristic of young
plants, they are referred to as JUVENILE leaves. Heterophylly such as this occurs in a
number of angiosperms as well.
The prefix Hetero- means _________________; the suffix -phylly means ___________ .
Observe a Pinus resinosa leaf cross section. This species of pine has lots of resin (no, duh!).
The mesophyll has lacks resin ducts in the mesophyll.
The epidermis has lacks cutin. (hint: look at the higher magnifications!)
The guard cells protrude from are even with are sunken below the epidermis.
How would you describe the shape of mesophyll cells? ______________________________
Inside the mesophyll there is an endodermis surrounding the vascular tissue that has
awesome Casparian strips; if you have not seen a strip well, this is your best chance this
What color are the Casparian strips? _____________________________________________
Between the endodermis and the vascular bundles there is a layer called transfusion tissue. Is
transfusion tissue is parenchyma collenchyma sclerenchyma .
Observe the xylem and phloem. The arrangement is radial collateral bicollateral .
Considering the position of xylem and phloem, the flat epidermis is the upper lower one.
Observe a cross section of a young pine stem. This stem is surrounded by pairs of leaves (also
caught in the cross-section). There are three views here at various magnifications.
The leaves face each other with upper lower epidermi in contact.
The leaf pair closest to the stem (at 1 o'clock) shows more leaves than just two.
This makes the whole collection of leaves a ________ shoot called a __________________.
The stem has a protostele siphonostele eustele . (hint: look at the higher magnifications!)
The xylem/phloem arrangement is radial collateral bicollateral .
The xylem maturation is endarch mesarch exarch . /16
A pith is is not present.
The cortex shows resin ducts and cells with lots of chemistry (take up the red dye).
The outermost layer of phloem is made of what kind of cells? _________________________
Observe a cross section of a maturing pine stem.
The epidermal functions are taken over by a ______________________________________ .
The cortex has lacks resin ducts. A secondary plant body is present absent .
A pith is present absent .
The color of the secondary phloem is ___________________________________________ .
The color of the tracheids in secondary xylem is ___________________________________ .
The secondary xylem shows (#)________ annual growth rings. (move to higher magnification…)
The blue strips radiating out through the secondary xylem are called __________________ .
Go to very high power to look at the blue strips. They are parenchyma sclerenchyma .
What is your evidence for this? _________________________________________________
Observe a cross section of a young pine root.
Is this an absorptive region of the root? yes no
What tissue has taken over the epidermal functions? _________________________________
What are the parenchyma cells just outside the xylem/phloem? ________________________
Is there an endodermis? yes no
The vascular cylinder is: diarch triarch tetrarch polyarch .
Observe a slide showing a longisection of a microsporangiate strobilus and relate what you
see on the slide to what may be available as a whole cone.
What processes occur in the microsporangia?________________and ___________________
The loose cells found in the mature microsporangia on this slide are microspores pollen .
What feature tells you which one it is? ____________________________________________
(Be careful about “true but irrelevant”)
What is the ploidy level of the microsporophyll? 1N 2N 3N ∞N
Observe a slide showing a cross-section of a microsporangiate cone and relate what you see
on the slide to the gross structure you have looked at. Three of the microsporophylls are
shown attached to the stem, and two of those are shown nicely.
How many microsporangia are there in each microsporophyll? one two more
What is the ploidy level of the sterile jacket? 1N 2N 3N ∞N
While here, look closely (very high magnification) at the loose cells inside the
microsporangium. Some of these are maturing and have become pollen grains.
Technically what is a pollen
grain?_____________________________ ____________________________________ /26
Also interesting on this microscope slide, is that the three attached microsporophylls show
their vascular connections. They each have a vascular bundle, but notice how the bundle
seems to head toward a space between stem vascular bundles (high magnification view).
This space caused by the departure of a leaf is called a _________ _________.
Observe a slide which shows mature pollen grains. The cellular composition of pollen grains
at the time of shedding from the microsporangium is: two disintegrated prothallial cells, a
generative cell, and a tube cell. The two wings are expansions of the outer layer of the
pollen-grain wall. There are three photos to view here.
The microsporocyte microspore pollen grain produced the "wings".
The generative tube cell has the larger cytoplasm inside the pollen wall.
What is the ploidy level of all cells in the pollen wall? 1N 2N 3N ∞N
(Be careful about “true but irrelevant” and remember that function needs an active verb!)
What is the function of the tube cell? _____________________________________________
What is the function of the generative cell? ________________________________________
•Observe the fresh specimens of megasporangiate cones of different ages. Dissect further, if
necessary, to determine the structure. Note that each "megasporophyll" is not really a leaf but
is a double structure: a bract with a flattened structure (called a CONE SCALE) in its axil. It
is on these cone scales that the megasporangia are borne.
How many megasporangia are there on each cone scale? one two few many
On which surface do they occur? upper lower
Observe a slide showing a longisection of a megasporangiate cone which is at the pollination
stage. Please do not use the stage knobs.
View the medium magnification view. The view depicts a megasporangiate cone at the time
of pollination (Spring 1). You can see a megasporophyll with a few resin ducts, and a
curved bract beneath. This is a compound cone scale. The ovule shown on the sporophyll
is in median longitudinal section. You can clearly distinguish the integument and its
micropyle. In this specimen the megasporophyll is not connected to the cone axis in the
plane of section.
Switch to the high magnification view. What is in the micropyle? ______________________
When pollen is being shed and carried by the wind in the spring, the young megasporangiate
(ovulate) cones open; pollen which sifts between the cone scales is caught in a drop of
fluid formed by the disintegration of cells at the tip of the nucellus. As the drop dries, the
pollen grains are sucked into the ovule. The transfer of pollen from microsporangium to
ovule is called pollination.
Most of what is contained inside the few layers of integument is nucellus. What word on
the generalized life cycle is equivalent to the nucellus? ____________________________
What is the ploidy level of the nucellus? 1N 2N 3N ∞N
Again, in the high magnification view. This is a near-median section of the nucellus inside
the integument. Note that there is a dome-shaped central portion, which is the nucellus.
If you look carefully in the middle of the nucellus, and focus clearly, you should find one
cell that is different from all the others. This cell has a larger and more obvious nucleus
with at least three nucleoli (red spots). It is the megasporocyte. Why is the nucleus larger
in this cell than those in
the cells of the nucellus? ____________________________________________________
What is the ploidy level of the megasporocyte? 1N 2N 3N ∞N
Observe the slide of Pinus young megasporangiate cones.
This slide shows a later stage (Summer 1). The micropyle has closed by growth of the
integument. There is a purple area in the nucellus that looks like it is disintegrating.
Observe at medium magnification…what is eating it? _____________________________
Deeper in the nucellus, the megasporocyte has divided meiotically and three of the meiotic
products degenerate, the fourth one remains as the functional megaspore. In the high
magnification view, the cell at the chalazal end is the functional megaspore; the
deteriorating meiotic products are at the micropylar end.
What is the ploidy level of the megaspore? 1N 2N 3N ∞N
What is the ploidy level of the disintegrating cells? 1N 2N 3N ∞N
Observe the Pine two-year megasporangiate cone l.s.
The view depicts a megasporangiate cone at the beginning of its second year (Spring 2). The
nucellus is further digested. The megaspore has been dividing slowly by mitosis without
cytokinesis. This is called a free-nuclear stage. You may ignore the partial collapse of
this cell... it is caused by the very large central _____________________________ .
The ovule below this one shows that organelle too (cropped reframed view)...it is light blue!
What is the ploidy level of each nucleus in this cell? 1N 2N 3N ∞N
This free-nuclear cell is technically the early stage of the ____________________________ .
Observe the longitudinal section of a Pinus archegonium with an egg.
This slide shows an ovule in Summer 2. The micropyle is to the right in the view. The
digested nucellus is nearly purple here. Contained in the nucellus is now a
megagametophyte. The free-nuclear stage has finally divided up to make perhaps 2000
cells. There are two archegonia shown in this slide. The upper one is cut at near-median.
You should be able to make out the sterile jacket and the neck cells above the egg.
Compare the size of the nucleus of a nucellus cell and a megagametophyte thallus cell.
Which one is smaller? nucellus megagametophyte
What is the ploidy level of the megagametophyte nucleus? 1N 2N 3N ∞N
The ventral canal cell has a large nucleus with a prominent red nucleolus, but the egg. Oh the
egg! How big is it? tiny same as the canal cell huge
The egg nucleus has how many nucleoli (red)? none one two three /12