Psilophyta - Psilotum Lab  

The Psilophyta have only two genera and a few species. They are found in the tropics. They may be terrestrial but are frequently found as epiphytes.

There are very few species in the Psilophya and they do not form significant components of ecosystems. However, they have many traits associated with fossils of the first terrestrial plants. Consequently, an understanding of their morphology and anatomy can help us to comprehend  the adaptations of  ancestral land plants. Psilotum species are composed entirely of stems. True Roots are not present in the Embryo, the mature Sporophyte or the Gametophyte. However. there is a perennial subterranean rhizome which gives rise to aerial shoots. The shoots have minute leaves. There has been much debate regarding the leaves. In most cases there is no vascular tissue in the leaves. Consequently, these structures have been called "Enations" or Prophylls. However, there are cases in which vascular tissue has been found in the leaves. Furthermore, reports of Leaf Traces in the Cortex of some plants lend credence to the argument that these are true leaves. The origin and development of Psilotum leaves is virtually identical to other vascular plants. Consequently, I believe that these are true leaves. They would be classified as Microphylls because they can have only one vascular bundle in each leaf, and there is no leaf gap.

Lab Activities

Observe the Rhizome system and note the origin of the aerial, photosynthetic stems.

Also note the Branching Pattern.

Where does Rhizoid production commence?

Examine free-hand sections prepared by us.

Stain these with Phloroglucinol & Toluidine Blue.
                                    (We will show you how!)

Phloroglucinol stains Lignin & Suberin Red/Orange

Toluidine Blue stains Lignin & Suberin Blue-Green.

Cells with lots of Pectins in the cell wall will stain Pink.

Locate the Rhizoids and note the presence of the Epidermis, Cortex, Casparian Strip, Phloem and Xylem.

Identify the type of Stele.

Use the Polarizing Filters to locate cells with thick cell walls.

Note the Branching Pattern.

Observe the Shoot Tip & note the clustering of the Leaves near the apex.

Note the White Flecks which exist in the depressions of the stem. Examine these with a stereo microscope. They are small but they are Very Important!

Locate the Sporangia and the forked leaves which subtend them.

Examine Commercial slides of Stem Cross-sections and locate

Examine  fresh stem cross-sections taken from the base of the stem.

a] Unstained with and without Polarizers

b] Stained with Phloroglucinol

Examine Commercial slides of the Sporangium and note the

uneven thickenings on the outer wall layer.

The small cells  split apart when the sporangia are mature.

Note the spores and their bean-like shape.

Demo - Fresh section through a sporangium showing the sporangial wall and spores.

Observe Demos which show Antheridia or Archegonia

What term is used when the Gametophyte and the Sporophyte look the same?

Examine the herbarium specimen of Tmesipteris.

What traits does it have in common with Psilotum?

What organ does the aerial stem resemble?