The term ` ` finishing fabric '' describes all boundary layers that delimit plant tissues on the outside or inside the plant. The primary closure tissues arise from the primary meristem , secondary closure tissues such as the periderm are formed from secondary meristems at a later point in time.
Primary finishing fabric
- already present in the seedling
- from the primary meristem formed
- undifferentiated tissue
The most important primary closing tissue in plants is the epidermis (skin tissue). It surrounds the shoot as a protective cover, which at the same time has to mediate the exchange of substances with the outside world. The primary closing tissue of the root is called the rhizodermis .
Characteristics ( scion )
- mostly one-shift
- there are more leukoplasts in contrast to chloroplasts
- wavy to jagged outline
- seamless interlocking
The outer walls of the epidermal cells are almost always thickened and also covered by a membrane called the cuticle , which is impermeable to water and gases, especially when a wax is still embedded or deposited.
Another primary closure tissue is the cutis tissue , which is created by subsequent corking of primary permanent cells , such as the epidermis, or - more often - seamlessly connected subepidermal parenchymal layers ( roots ). The endodermis always delimits tissue areas from one another. For example, it is regularly found in the root, where it separates the central cylinder from the bark.
Secondary finishing fabric
If the epidermis cannot cope with a strong growth in the thickness of the plant organs , as occurs, for example, in woody plants , through corresponding dilation growth (tangential expansion growth ), it is destroyed and often replaced by secondary closing tissue. The subepidermal cell layer usually gives rise to a sequel, the cork cambium or phellogen. This gives off tightly packed, quickly corking, often thick-walled cells without intercellular cells , the cork . Inwardly, chlorophyll- containing bark cells , the phelloderm, arise, often in small numbers . Cork, phellogen and phelloderm are collectively referred to as periderm (cork fabric). The gas exchange through the seamless, intercellular-free cork layer is made possible by lenticels or cork warts. These represent closely circumscribed areas of tissue in which, instead of cork cells, intercellular filling tissue has formed, which consists of large parenchymal cells. The intercellulars of the lenticels enable a connection between the intercellular system of the plant and the outside air. The lenticels can often be seen as line or pustule-shaped elevations with the naked eye on the branches of many wooden plants . The first cork cambium soon ceases to be active in plants that grow thickly, for example in most trees. It is replaced by a second cork cambium, which is formed in deeper layers of tissue. This too is only active for a limited time and is replaced by a third one and so on. The entirety of these cork layers is called the bark . Since the process of bark formation soon spreads from the primary bark to the bast , the new cork layers are usually separated by layers of bast cells . This results in a layered structure that is usually already visible macroscopically, as the individual layers of cork, which are of course closed off from the supply of water and nutrients, quickly die off and soon become detached in layers.