Tree in 3-D Lab

1. ENVI 202 - Tree Biology

Module B1 10  Identify and locate the different tissues found in a transverse section of oak or elm wood

Illustrate and describe the significance of the results after the application of I 2KI to the wood surface

Identify and locate the tissues from the radial and tangential views

• Investigation
• Purpose

To cleanly and clearly expose tissues found in the woody sections of trees for study.

• Materials Required
• Hand saw
• Sharp knife - like a hunting knife
• Single or one-edged razor blades
• Bread board to perform cutting
• First-aid kit
• Rubber gloves

The procedure to follow is described below.

Tissues in a Transverse Section Cutting a Transverse Section

Saw a slice of wood from the branch or trunk provided, using a hand saw. The slice should be near 1.5 cm in thickness. Do not sand the wood. By using an electric planer or a sharp knife - use extreme caution - slice/clean off the surface of one side of the wood to expose the vessels. Do another slicing this time with a one-edged razor blade.

The entire surface need not be cleaned. (A pie-section should be clean, the pith being the center point.) Check with your instructor to see if the exposure is clear enough. Otherwise nothing will be seen and it will be a most frustrating experience.

2. 11

ENVI 202 - Tree Biology Module B1 Identify the following tissues:

Bark/Epidermis Phellum-outer bark, bark cambium or phel- logen-greasy looking, phelloderm

Cortex tissue Green layer.

Phloem Grit cells like crystals.

• Vascular Cambium

Xylem Vessels The vessels are arranged in and axial di- rection (up and down) so in the transverse section view, they appear as large and small holes. Only the most recent year will have open vessels that function in mineral and water transport.

Pith Will appear shiny and flaky, like sponge toffee.

• Growth Increment

Earlywood/Latewood Large vessels indicate those formed at the beginning of the growing season. Smaller vessels develop later in the season. The large vessels are earlywood, the small are late- wood. In elm, the wood will have character- istic white, “wormy” lines throughout. These are latewood vessels in elm.

Illustrate and label the tissues listed above

3. ENVI 202 - Tree Biology

Module B1 12 Apply I2KI Apply the I2KI (Iodine in Potassium

Iodide) to a “Pie Section” of the Transverse Section

Mix 0.3 g I crystal, 1.5 g KI solution, in 100 ml H2O. Shake well. This solution will stain only the starch that are in living cells. The stain is purple. This solution is extremely poisonous - do not allow contact with skin and do not ingest. Wash hands thoroughly after application especially before eating, drinking, smoking, etc.

Draw and colour a diagram of your observations.

The I2KI solution, when applied to the wood, will turn bluish-purple

Identify and locate the different tissues found in a transverse section of oak or elm wood

 Illustrate and describe the significance of the results after the application of I 2KI to the wood surface

Identify and locate the tissues from the radial and tangential views

Image source: Olds College Observations after I2KI Application

Image source: Olds College

4. 13

ENVI 202 - Tree Biology Module B1 when there is a presence of starch. Starch (carbohydrates) will only be stored in living cells called parenchyma cells. Looking at the “purple” reveals the network of symplastic compartments - boxes within boxes within boxes. The purple dots are the cross-section of the axial paren- chyma. Most of the purple will be in the last five or six rings. Every purple dot is a battery of stored energy.

The cambial zone will not show any purple. (If it is, check with the instructor to ensure a better cleaning of the sample.) The cambial zone does not store energy - it uses energy.

The vascular cambium is widest and therefore best viewed in the spring during active growth. In the spring, the vascular cambium is several layers thick and can be seen easily with the aid of a dissect- ing microscope. At any time, the vascular cambium can be witnessed by pushing the cross-section of wood with an inward push using the thumbs and forefingers. A clear watery gel-like substance will be squeezed out revealing the location of the vascular cambium layer.

The vessels themselves will not have any purple but they are surround- ed by parenchyma cells that will be purple, full of stored energy.

5. ENVI 202 - Tree Biology

Module B1 14 Radial and Tangential Sections Cutting the Radial and Tangential

• Sections

Take the transverse section of wood you have been investigating and cut it across through the pith. Lay the sharp edge of the large knife an top of the wood and gently hit the knife downwards through the wood with a mallet or sledge. This exposes the radial view. Discard one of the pieces of wood.

Take the knife and cut down at the edge of the piece, cutting just with- in the last one or two growth increments.

Do not clean or shave these views. Apply the I2KI immediately.

Illustrate and label from the radial view

Fibres Are arranged axially and remain clear Vessel Elements Plugged and unplugged

• Radial and Axial

Parenchyma Weaves in and out like a basket Pith Identify and locate the different tissues found in a transverse section of oak or elm wood

Illustrate and describe the significance of the results after the application of I 2KI to the wood surface

 Identify and locate the tissues from the radial and tangential views

Image source: Olds College

6. 15

ENVI 202 - Tree Biology Module B1 Illustrate and label from the tangential view.

Ray Parenchyma Appear as basket weaving.

Image source: Olds College