"Simple" Tisues - Parenchyma - Collenchyma & Sclerenchyma
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This lab is designed to give you information on the primary nonvascular tissues. These are relatively simple compared to xylem and phloem. However, we will see that there is a considerable amount of variation within these tissues. In addition, you will observe the major components of the protoplast that are visible with the light microscope.

Study cell shape, contents, and wall structure, the relation of cells to one another for intact tissues, the presence of intercellular connections via pits, and the presence or absence of intercellular spaces. The cell walls and air spaces constitute the Apoplast. The Plasmalemma and all within it constitute the Symplast. These are Extremely Important concepts, which must be appreciated to understand Plant Physiology!

Within the Symplast, look for the cytoplasm, nuclei, chloroplasts, other plastids, crystals, and vacuoles colored with anthocyanins. Use polarizing filters to locate starch grains and crystals. Also use polarizers and stains to study cell wall organization and composition.


Cortex of Pereskia stem:


Parenchyma consists of relatively large, thin-walled cells. The cells are arranged loosely, that is, there are intercellular spaces among them. The protoplasts of these cells contain chloroplasts. Some of these cells may have amyloplasts and crystals. Pereskia is a member of the cactus family. It has spines but it also has normal leaves. Its flowers are extremely beautiful like those of most cactaceae.

Young leaf of Elodea.


Aerenchyma & Stellate Parenchyma

A strikingly different shape of parenchyma cells is illustrated by stellate parenchyma. These are branched and adjacent cells are connected with each other by means of the branches. Parenchyma composed of branched cells is highly lacunose; that is, it has a large volume of intercellular space. The spongy layer in leaves has branched cells with large intercellular spaces. The term Aerenchyma is often used to describe parenchyma, which has large air spaces.

Cyperus papyrus stem stained with IKI

Aerenchyma in Cyperus javanicus

Cyperus papyrus

Cyperus laevigatus

Aerenchyma can be found in the stems of other members of the Cyperaceae, like C. laevigatus (makaloa). Makaloa stems are smooth and resilient. The Aerenchyma is like foam rubber on a microscopic scale. Makaloa stems were used to make fine sleeping mats by ancient Hawaiians and the qualities of their Aerenchyma contributed to their utility.

Sample from a makaloa mat: Note the Air Spaces (A)

Canna Flowers

Pineapple leaves also contain stellate parenchyma. What functions are suggested by the 3-dimensional shape of these cells?

Canna Petiole Cross Section

Stellate Parenchyma Cells

Endosperm Cells: The parenchyma cells you have examined thus far have relatively thin walls, but there are also thick-walled parenchyma cells.

Persimmon Endosperm

Endosperm with Large Pits

You have already observed cytoplasm and chloroplasts. Other protoplast components include several more types of plastids, vacuoles, and various kinds of crystals.

Chromoplasts and Pigment Bodies. They may be yellow, red, and orange colored plastids and similarly colored crystal-like bodies. The latter are called pigment bodies because there is some question whether they may be classified as plastids.

Chromoplasts from Red Pepper (Capsicum)

Chromoplasts from Flower Petals

Red Bell Pepper Fruit

The color of Alamanda Flowers is due to Chromoplasts

Leucoplasts are mysterious and difficult to demonstrate without special techniques.

Amyloplasts are filled with starch, which sometimes occupies the entire organelle. They are also regarded as Leucoplasts because they lack color.

Leucoplasts clustered around the Nucleus of a Parenchyma Cell stained with Toluidine Blue

Unstained potato Amyloplasts

Commercial slide of Potato Amyloplasts

Amyloplasts from Canna seen with normal illumination

Amyloplasts from Canna seen with crossed Polarizers

Amyloplasts stained with IKI

"Statoliths" are amyloplasts, which contain many large multifaceted starch grains, similar to those above. Their function may be related to gravity perception.

Non-cytoplasmic Contents

Anthocyanins in a surface view of Epidermal Cells

Zebrina Leaves: The Anthocyanins are on the lower surface of the Leaves. I wonder what they are doing down there????

Crystals are vacuolar in nature.

Druse Crystal seen with Bright Field Illumination

Druse Crystals seen with Crossed Polarizers.

Raphides in an isolated Vacuole seen with crossed Polarizers

Raphides on the Loose!!!!

The function of these crystals is relatively uncertain. They seem to be more abundant in plants, which grow in arid and xeric environments. They are all composed of Calcium oxalate, which causes epithelial cells to swell. Consequently, they should deter herbivory.


Collenchyma is closely related to parenchyma. However, the plastids are not well differentiated in collenchyma while they are well differentiated and obvious in parenchyma. Collenchyma always occurs just beneath the epidermis, while parenchyma occurs throughout the plant. Collenchyma cell walls are unevenly thickened. When the thickening occurs at the corners where cells are joined it is called angular. Lamellar collenchyma has thickenings on their tangential walls, which are parallel with the surface. Lignin is usually not present in collenchyma.

Unstained Collenchyma in Widelia Stem

Collenchyma stained with Toluidine Blue

Unstained Collenchyma in Celery

Unstained Collenchyma in Celery


The distinction between parenchyma, collenchyma and sclerenchyma is largely based on the wall structure. Parenchyma cell walls are usually thin and primary while in sclerenchyma a secondary wall is formed on the inner side of the primary wall. Secondary walls are those, which develop after a cell, has ceased to enlarge. Collenchyma cells have secondary wall thickenings but these are uneven in their distribution. Furthermore, the cellulose fibrils in Collenchyma are not as highly organized or tightly bound as in Sclerenchyma. Finally, Sclerenchyma cells can be found in many locations throughout the plant body but Collenchyma are always just beneath the Epidermis.

Sclerenchyma cells are usually classified into sclereids or fibers on the basis of form as well as the abundance and type of pitting.

Sclereids are generally shorter than fibers and their walls show more abundant pitting. The pits are often branched (ramiform). Walls of sclerenchyma cells are usually lignified and, therefore, stain red with safranin or phloroglucinol-hydrochloric acid. They often show concentric laminations, which indicate different periods of wall synthesis. Sclereids vary in shape and occur in all parts of the plant.

Fibers tend to be highly elongated cells with tapering ends, and they often occur in bundles. There are few pits in the walls of fibers. The pits, when present, are usually simple and unbranched.

In studying Sclerenchyma observe their (1) overall shape;
(2) wall structure; (3) pits; (4) staining reactions to Phloroglucinol & Toluidine Blue; (5) appearance with crossed polarizers.


Cross Section of Hoya Stem stained with Toluidine Blue: The sclereids occur in a unicellular band in the outer part of the stem.

Solitary Sclereid on Hoya Stem stained with Toluidine Blue

Various Wall Layers in Sclerenchyma

Elongated Sclerids in Onion Bulb Scale

Cross section of Podocarpus Leaf

Astrosclerids from Nymphaea Leaf

Sclereid from Podocarpus Leaf

Partly Dissected leaf showing Trichosclereids

Trichosclereids from Olive Leaf


Cluster of Brachysclereids

Solitary Brachysclereid


Like sclereids, fibers may be found in various parts of the plant. Fibers are particularly common near the phloem (phloem or bast fibers) and the xylem (xylem fibers). In monocots fibers often enclose vascular bundles (fibrovascular bundles) or appear as strands that are independent of vascular tissues.

The best commercial fibers are usually associated with the phloem. This includes hau (Hibiscus tiliaceus) and wauke (Broussonetia papyrifera) plus Cannabis. Coarse fibers can be obtained from monocot leaves like uki uki grass (Dianella sandwichensis) and Agave. Agave was grown in Hawaii but was uneconomical. Some of these plants have escaped cultivation and can be found in nature. They are slow growing but once established, they may be difficult to eradicate. This could present a problem for native species if they can't compete with Agave.

The phloem fibers of this plant were used by ancient Hawaiians for making rope.

Unstained hau fibers from an Hawaiian artifact

Hau fibers stained with Phloroglucinol & viewed with crossed polarizers

Cross sections of flax stem that show the phloem or "bast" fibers which are green. In this case the green color indicates the absence of Lignin.

Cannabis stem cross section

Highly Magnified Fibers

Fiber from Oak wood

Our Favorite Sclereid!!!!!

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