Plant Histology

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In botany , the sclerenchyma is a supporting tissue of some plants composed of cells dead at maturity, which are thickened secondary walls are so thick and hard. Its name comes from the Greek escleros , "hard" and enchyma , "substance".
Is an elastic fabric, ie it may be deformed but returns to its original shape. The compound that gives it its characteristics sclerenchyma cell wall is lignin , present in greater or lesser extent in the cell walls of all vegetables . Provides high resistance to plant parts that have stopped growing. In some cases serve as a means of defense, and that give the plant resistance against the attacks of insects . Sclerenchymatous cells differ from the collenchyma secondary walls that have lignified and generally that when adult, often lack protoplast .
The sclerenchyma comprising:
Fibers : are spindle-shaped cells, ie cells with polygonal ends long and sharp. They have few pits (holes coupled to two adjacent walls cross the cell-cell, communicating). The fibers were classified as:
Xilemáticas : part of the xylem fulfilling its role of support. There are three types of fibers ...
... xilemáticas: fibrotraqueida, fiber and fiber libriform partitioned.
Extraxilemáticas : correspond to the phloem or bast (bast fibers) or forms cortical groups or rings. In the monocots is the main supporting tissue, and can form rings and cords subepidermal and / or cortical, and sheaths surrounding the vascular bundles (veins).
Sclereids : often are shorter than the fibers have no sharp ends, take various forms and often derived cell parenchyma esclerificadas. They are found in various plant organs: leaves, fruits, seeds, etc.. They are classified according to their shape:
Sclereids or stone cells : more or less isodiametric, thick-walled, small lumen simple and branched pits.
Astroesclereidas : star-shaped, common leaf Camellia .
Macrosclereid .
Osteoesclereidas : bone shaped.
Filiform sclereids : common olive leaf ( Olea europaea ).

A rare species is an organism that is very rare or scarce. This designation can be applied to taxa of plants and animals, and may be different from the term " endangered species "or" endangered . "
The designation of a kind rarely can be made ??by an official organization as a national, state or province. However, the term is most commonly used without reference to specific criteria. The IUCN designates not normally, but can use in their scientific discussions. 1
The concept of rarity is set to have a very small number of individuals, usually below 10,000, but the concept is also influenced by having a very narrow geographic distribution of endemism and / or fragmentation of habitat . 2
A species may be threatened or vulnerable, but not considered rare if, for example., Have a large population, dispersed, but their number declines rapidly or is predicted that. Rare species are generally considered threatened simply because of their inability to recover small population of events stochastic and the potential for rapid decline of its population.

A spike is a type of inflorescence racemose in which the shaft or rachis is elongated and the flowers are sessile, reaching younger flowers at the apex of it.
Examples of species that have spike inflorescences are plantain ( Plantago ), pineapple or pineapple ( Ananas ) and gladiolus ( Gladiolus ).
According to the shape and size of the spine can distinguish several different types of spikes. Thus, Ananas , the spike is oblong and the terminal bud is vegetative. In Plantago , the pin is cylindrical and Gladiolus is statistical.

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