Simple Tissues

• Ground tissues, sometimes called simple tissues, since they are composed of only 1 cell type

• Ground tissues make up the bulk mass and strengthening elements of the plant body

• There are three main types of ground tissues in plants:

Parenchyma

• Parenchyma serves as the bulk material and storage area for plants

Collenchyma

• Collenchyma is a tissue used for flexible support in stems or petioles

Sclerenchyma

• Sclerenchyma is a tissue used for rigid support in stems or petioles

Parenchyma

• From para meaning "beside", and chyma meaning "in-filling", referring to the nature of parenchyma to fill-in around the other tissues

Function

• Parenchyma serves as the main storage tissue for plants

• It also serves as the bulk structural tissue of roots, stems, and leaves

Features

• These cells are usually thin-walled, usually lacking secondary walls

  • In some cases of stress, plants can add lignin to parenchyma, strengthening those areas (called lignified parenychma)

• They are isodiametric in shape; they are an equal diameter in all directions

• Parenchyma cells are alive at maturity conducting cellular processes, unlike xylem and sclerenchyma

• Parenchyma is the most abundant cell type in a plant

Parenchyma sub-types

Aerenchyma

• Parenchyma tissues with abundant air spaces are called aerenchyma

• The spongy mesophyll of a leaf, where gas exchange occurs near stomata, is a common site of this tissue

• Many aquatic plants possess aerenchyma in stems to shuttle oxygen to roots for respiration in anoxic, water-logged soils

Chlorenchyma

• Parenchyma tissues with many chloroplasts are called chlorenchyma

• The palisade layer of a leaf, where light interception occurs for photosynthesis, is a common site of this tissue

• Many herbaceous stems also exhibit chlorenchyma to contribute to the photosynthesis of the plant

Collenchyma

• From kolle meaning "glue", and chyma meaning "in-filling", referring to the flexible but supportive nature of collenchyma

Function

• Collenchyma provides flexible support in stems or petioles

Features

• Collenchyma has an irregularly-thickened primary wall

• These cells are found under the epidermis (i.e. centrifugal direction), in herbaceous stems and some leaves

• Many plants in the Lamiaceae, with square stems, use collenchyma for stem support

• Collenchyma cells are alive at maturity conducting cellular processes, unlike xylem and sclerenchyma

Sclerenchyma

• From skleros meaning "hard", and chyma meaning "in-filling", referring to the rigid or hardened nature of sclerenchyma

Function

• Sclerenchyma fibers provide rigid support in stems

• Sclerenchyma sclereids provide hardened protection in fruit pits and leaves

Features

• Cells have evenly-thickened secondary walls

• These cells have a very small lumen (interior space), compared to xylem cells

• Sclerenchyma cells are dead at maturity

• Many herbaceous stems use sclerenchyma tissues to strengthen weak areas, such as around primary phloem

• The strength of bamboo, comes purely from sclerenchyma, and not from wood!

Sclerenchyma sub-types

Fibers

• Fibers are long and thin in shape

• They are evenly-thickened in cross-section with a small or no lumen

• Fibers are found longitudinally in stems, roots, and leaves

Sclereids

• Sclereids are roughly the same length and width

• These cells are found in "pockets" of fruits, seeds, stems, and leaves

• Sclereids create strength and/or a deterrent to herbivores that may damage embryos, stems, and leaves while feeding