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