Scleroid
A sclereid or sclerenchymal cell ( ancient Greek σκληρός sklēros , German 'hard' ) is a mostly dead cell in plants that has a strongly thickened cell wall , but is not fibrous. Sklereids are often used to strengthen and strengthen parts of plants. They can appear individually (as an idioblast ) or form a firming tissue ( sclerenchyma ). Sklereids have a thick secondary cell wall that is severely lignified . They have numerous simple pits . Their shape is very variable.
Occurrence
Sklereids occur in the epidermis , in the basic tissue and in vascular bundles .
In the shoot axes , sclereids often occur in the form of a sclerenchymal cylinder around the vascular bundles and often arise from parenchymal cells. In the bark of trochodendron or Pseudotsuga taxifolia , branched scleriids can also be found.
In leaves sclereids come in many forms. There are two distribution patterns in the mesophyll: diffuse distribution in the leaf tissue (e.g. in Olea or Pseudotsuga ) or limitation to the ends of the small vascular bundles ( e.g. some Polygalaceae , Capparaceae , Rutaceae ). The star-shaped scleriids of the Nymphaeaceae protrude into the large intercellular spaces of these species. The sclereids of the olive tree ( Olea europaea ) are exceptionally long at around one millimeter.
The fruits of pears ( Pyrus ) and quinces ( Cydonia ) have stone cells distributed in the pulp. The pits are often branched, as two pits unite inward during cell wall growth. In the case of apples ( Malus ), sclerids sit in the core.
In seeds , the hardening of the seed coat often occurs because the epidermis and, in some cases, the cell layers underneath develop into scleraids.
to form
According to their form, the following subdivision can be made:
- Brachysklereids or stone cells are approximately isodiametric. They occur in groups mainly in fleshy fruits. In nut fruits and stone fruits they form the hard layer.
- Makrosklereiden or rod cells are elongated cells and especially occur in fruit and seed trays. This also includes the Malpighian cells of the butterflies .
- Osteosklereids are elongated cells and broadened or lobed at the ends. They occur especially in leaves.
- Astrosklereids are branched, often star-shaped cells. they occur particularly in the leaves of the Nymphaeaceae and some monocotyledonous aquatic plants .
- Trichosklereids are long, pointed, hair- shaped , sometimes slightly branched cells.
supporting documents
- Gerhard Wagenitz : Dictionary of botany. The terms in their historical context. 2nd, expanded edition. Spektrum Akademischer Verlag, Heidelberg / Berlin 2003, ISBN 3-8274-1398-2 , p. 297.
- Katherine Esau : Anatomy of Seed Plants . John Wiley, 1960, pp. 55-58.