Secretory Ducts and Cavaties

Secretory Ducts and Cavities
Link to Laticifer & Nectary Lab

Secretory Cavities are localized areas that contain secretions.

They differ from Secretory Ducts which are highly elongated and extend over a large distance in the organ. These occur primarily in stems and leaves as well as fruits. The types of secretory products vary but oils and resins are common.

These may be shizogenous or lysigenous. The presence of a well-defined epithelium usually indicates the former. Because lysigenous cavities develop by cell lysis, an epithelial layer is usually absent. Furthermore, cell wall fragments that produce an irregular perimeter indicate shizogeny.

Secretory Cavities

Citrus Fruits

Observe the rind with your dissecting scopes.
Make sections of the rind and view unstained. Locate the Secretory Cavities. Do these appear to be shizogenous or lysigenous?
Study commercial slides and compare with fresh sections.


Citrus Flowers	Young Citrus Fruits	Citrus Rind

‘Ohia‘a lehua Leaves

Place a leaf on a microscope slide and view this with the 4X objective of your microscope.

Use the Weboski method to study the Secretory Structures.

Flip up the swinging condenser lens.

Turn up the illumination to full.

Look for round, yellow areas. These are the secretory cavities.

Examine cross sections of the leaves and locate these cavities.


Ohi'a Lehua Leaf Cross Section Unstained	Secretory Cavity after Toluidine Blue Staining

Floral Bracts of Cotton

Use the Weboski method to study floral bracts of Cotton.
Why don't you need to use stains to observe these secretory structures?

Secretory Ducts (Canals)

Pinus Stem & Leaf

Locate the Secretory Ducts

Observe cross sections of the Leaf. View unstained then stain with Sudan. These contain resin and are often referred to as "Resin Canals". However, they are Secretory Ducts in the general sense.
Observe Commercial Slides & compare with fresh Sections.
Do the same for the Stem.
Observe the DEMO Longitudinal Section prepared by your intrepid lab instructor!

Araucaria (Norfolk Island Pine)

Explore hand-sections through the leaves on young stems and locate the Secretory Ducts.
These should resemble those found in Pinus.

Pinus ponderosa Pine Needles (Leaves)	Araucaria sp. Araucaria Foliage
Cross Section of a Pine Needle: Note the Secretory (Resin) Canals.	Note the Well defined Epithelial Layers on the Secretory Canal above.

Cross Section of a Young Pinus Stem with Leaf Base: Note the Secretory (Resin) Canals in the Stem.

Demonstration Slides (Time Permitting)

Observe various slides that illustrate Secretory Cavities and Ducts.

kukui (Aleurites moluccana)

This plant plays an important role in Hawaiian culture. Ancient Hawaiians used virtually every part of this plant as an adhesive, for lamp oil, as waterproofing, as polish for storage vessels, in fire making, in lei making, in kappa making and in healing. It is still used to make fine leis. Many of its useful features are derived from the "oil" which can be obtained from its stems, leaves and fruits.

Your challenge is to determine what type of secretory structure produces this oil!

You will examine hand sections to solve this puzzle.
Study unstained transverse and longitudinal sections from the petiole near its junction with the leaf blade.
Answer the following questions to solve the riddle.

Transverse Sections: Locate the red-brown areas.

In what regions or zones are they located?

What accounts for their color?

Are they one cell wide or many cells wide?

Are the secretory cells greatly enlarged compared to surrounding cells?

Is there evidence for a secretory epithelium?

Longitudinal Sections: Locate the red-brown areas.

Are the secretory cells rotund, truncated (short & rectangular) or highly elongated?

Do they form discontinuous secretory cavities or elongated, continuous channels?

Are they branched or un-branched?

Identify the Mystery Secretory Structure!!!!!!

Link to Laticifer/Nectary Lab