Bio 11 – Exercise 6 – The Stem

1. Study a freshly cut stem of an herbaceous and woody dicot and a monocot plant

1.2 What stem has the most prominent node and internode? Why?

Dicot.

2. Study a vigorously growing coleus plant.

2. 1 Where do new leaves and internodes originate?

Nodes.

3. Study a longitudinal section of a coleus shoot apex under the LPO and observe the following: promeristem, leaf primordium, and primary meristems.

3.1 Tabulate the differences between a shoot tip and root tip.

Root tip has neither a leaf primordia nor axillary buds. Shoot tip has no root cap.

5. Follow the subsequent development of the stem tissues by examining cut sections from the uppermost to the lowermost internodes of coleus.

5.1 In which internode do you find differentiated tissues?

Lower internodes.

6. Study a prepared slide or free-hand section of a monocot stem.

6.2 How do primary tissues of this stem differ from those in coleus?

Monocot vascular bundles are scattered and the ground tissue isn’t partitioned into pith and cortex.

7. Focus on a single vascular bundle of a monocot stem under the LPO.

7.2 What is the pattern of xylem differentiation in the stem?

endarchy

7.3 Tabulate the anatomical differences between a monocot and dicot stem.

Monocot: scattered vascular bundles, no distinction between pith and cortex, no cambium, no secondary thickening.

Dicot: vascular bundles in a ring

8. Examine prepared slides of a woody dicot and pine stems. Study the different tissues under a compound microscope.

8.1 Which tissues constitute the bulk of the stem?

Secondary xylem

8.2 What tissues may have produced the additional cells? How do you account for this?

Vascular cambium. Secondary growth.

8.3 What protective tissue)s) is/are present in your specimen?

Periderm

8.4 What do you call the region with the loosely arranged parenchyma cells? What is its function?

Lenticel for gas diffusion.

8.5 Do you see companion cells and vessel elements in the pine stem?

Yes

8.6 Do you observe resin ducts and secretory cells in your specimens?

Yes

9. Examine cross, radial and tangential sections of a dicot and pine wood.

9.1 Differentiate the arrangement, shape and size of the wood rays in each section of the two specimens.

Cross section: Thin strands

Radial: Box-like

Tangetial: Pod-like

9.2 Tabulate the similarities and differences between a dicot and pine stem

Dicot: No resin canal

10. Examine various modified stems

Plant Specimen – Modification – Function

Water hyacinth – Enlarged – Buoyancy

Potato – Tuber – Storage and Vegetative reproduction

Ginger – Rhizome – Storage

Grass – Stolon – Vegetative reproduction

Cactus – Photosynthetic stem – Photosynthesis

Notes:

Some answers differ for each class/group. You need to do the experiment.

For Table 6.1: Only monocot has leaf sheath and no petiole, only woody dicot has lenticels.

For 7.1:

From subtlerainbow's Multiply album.