Weed Anatomy, First Edition. Hansjoerg Kraehmer and Peter Baur. © 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

8

Chapter 2

Parenchyma

In animal histology, parenchyma is the tissue in which organs are embedded. In plants, parenchyma

cells make up the bulk of the organs and are often found as a sort of filling material, for example in the pith. They are characterised as isodiametric in some textbooks. This is true for many cases but not for all. It is rather difficult to measure a diameter within the spongy mesophyll of leaves. One characteristic of parenchymatic cells is that their cell walls are usually

Figure 2.1Parenchymatic cells in the cortex of an Echinochloa crus-galli (L.) P. Beauv. root.

Intercellularspace

thin (∼0.2 to 2 µm in diameter; this figure results from different published data, for example from Schopfer and Brennicke 2006 and Taiz and Zeiger 2007). Parenchyma is living tissue, it contains complete pro-toplasts. These cells keep their ability to divide and most look undifferentiated. Typically, they are sur-rounded by intercellular spaces or larger cavities for effective gas exchange (Figure 2.1).

Figure 2.2Chlorenchyma cells in the stem of Galium aparine L. Intercellular cavities (arrow) facilitate gas exchange.

9Chapter 2 Parenchyma

Figure 2.3Chlorenchyma cells from the stem of G. aparine L. with chloroplasts.

Figure 2.4Six-rayed stellate parenchyma cell in the pith of Juncus effusus L.

A special form of parenchymatic tissue is the chlo-renchyma (Figures 2.2 and 2.3). It contains chloro-plasts and is often located close to the surface of assimilating stems. The leaf mesophyll consists mainly

of chlorenchyma cells. Intercellular cavities facilitate gas exchange. This is particularly pronounced in the aerenchyma of plants living in water where it consists of stellate cells, as shown in Figure 2.4.