2.2 Ground tissues

The main tissue types of the ground tissue system are parenchyma, collenchyma and sclerenchyma. Parenchyma have thin walls of cellulose, whereas collenchyma have cell walls with thickened areas of additional cellulose. Sclerenchyma cells have lignified cell walls. They can be further categorised into narrow long cells (fibers) and cells of various other shapes (sclereids).

2.2.1 Parenchyma

Figure 2.3.a. Parenchyma cells with blue green thin cellulose cell walls.

Figure 2.3.b. Parenchyma cells with blue green thin cellulose cell walls
Figure 2.3. Parenchyma cells with blue green thin cellulose cell walls.

When parenchyma cells are modified to create tissues with air spaces for buoyancy or aeration of tissues, then the tissue is described as aerenchyma rather than parenchyma.

Figure 2.4. Aerenchyma in the stem of the aquatic monocot Potamogeton
Figure 2.4. Aerenchyma in the stem of the aquatic monocot Potamogeton. Large air spaces can be seen between the cells of the cortex. There is a single layer of epidermal cells and behind that a single layer of cortical parenchyma cells, then aerenchyma tissue for buoyancy and movement of oxygen to the submerged tissues.

2.2.2 Collenchyma

Figure 2.5.a. Fraxinus collenchyma
Figure 2.5.a. Collenchyma cells of Fraxinus. Upper cells are parenchyma, collenchyma with large dark cell walls and squat rectangular dermal cells at lower surface.
Figure 2.5.b. Collenchyma cells in celery
Figure 2.5.b. Collenchyma cells in celery that are unstained and have large white cell walls.

2.2.3 Sclerenchyma

Sclerenchyma cells have lignified cell walls.  They can be of two broad types: sclereids and fiber cells.

2.2.3.1 Sclereids

Figure 2.6.a. Sclerenchyma cells with thick cells walls that are stained red due to lignin in the cell walls
Figure 2.6.a. Sclerenchyma cells with thick cells walls that are stained red due to lignin in the cell walls.
Figure 2.6.b. Sclereid cells or stone cells in the pear fruit. The sclereid cells have thick red stained cell walls are surrounded by blue green stained parenchyma cells
Figure 2.6.b. Sclereid cells or stone cells in the pear fruit. The sclereid cells have thick red stained cell walls are surrounded by blue green stained parenchyma cells.

2.2.3.2 Fibers

Fiber cells are sclerenchyma cells that are long and thin.

Figure 2.7. Drawings of stone cells from the coconut shell and fiber cells from the bark of Sambucus nigra.
Figure 2.7. Drawings of stone cells from the coconut shell and fiber cells from the bark of Sambucus nigra. The microscopy of vegetable foods, with special reference to the detection of adulteration and the diagnosis of mixtures.

 

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