Evolution of Vascular Plants

Evolution of Vascular Plants  The sporophyte is independent and long-lived Like all land plants, vascular plants have Haplodiplontic “generational rotation”, with haploid gametophytes and sporophytes diploid. However, unlike liverworts, hornworts, and true mosses, Vascular plants have a dominant, free-living, sporophyte generation. photosynthetic, and relatively persistent, although, hornworts have a sporophyte which is also photosynthetic and relatively long-lasting. In all land plants, The sporophyte is initially attached to and nutritionally dependent on the gametophyte. However, in vascular plants, the sporophyte soon grows larger and become nutritionally independent, then the gametophyte dies.  Branched Sporophyte The sporophyte axis, or vascular plant stem is different from liverworts, hornworts, and mosses because they branch and contain many sporangia (not just one). The earliest vascular plant stems has dichotomous branching, where the apical meristem is divided into two, identical meristems, each of which grows independently more or less the same. Subsequent offspring develop the pattern modified growth, called pseudomonopodial, is initiated dichotomous, but then one branch becomes dominant and surpasses the other other, lateral emerging branches . Plant descendants subsequent vascular growth develops monopodial growth (See Euphyllophyta).  Ligninated Secondary Cell Wall Vascular plants develop lignin, is complex polymer of phenolic compounds. Lignin is incorporated into the wall layer additional cells, known as secondary walls , which found in specialized cells of vascular plants. Secondary wall secreted outside the plasma membrane (between the plasma membrane and the cell wall primary) after the primary wall is secreted, which is also after the cell stops elongated. Secondary cell walls are usually thicker than primary walls and, like the primary wall, contains cellulose. However, in secondary walls, lignin is secreted into the spaces between cellulose microfibrils, forming a kind of cement that binds each other.  Sclerenchyma Sclerenchyma (Schelenchyma: Gr. scleros, hard + enchyma, infusion, refers to infusion of lignin in secondary cell walls) is nonconductive cells that have cell walls thick and lignified secondary, usually with holes, and dead when mature. There are two types of sclerenchyma namely (1) fibers, which are cells long and very narrow with walls sharply tapered tip; and (2) sclereid, whose shape is isodiametric to not regular or branched. Fiber functions in support mechanics of various organs and tissues, sometimes forming a large part network. Fiber often occurs in clusters or bundle. This fiber could be components of xylem and/or phloem or can occur independently of the network vascular.  Trachea (xylem) Vascular plants, as the name suggests, have a network of vessels true, consisting of cells that have become highly specialized for fluid conduction. Vascular tissue represents a major adaptive breakthrough in plant evolution; more efficient conductivity allows high evolution plants and a much greater diversity of forms. Soecialized cells or tracheal elements function in the conduction of water and mineral. The tracheal elements are generally elongated cells dead at the time mature and have a secondary cell wall that is lignin. These cells connect end to end, forming a channel structure long. The trachea is usually associated with parenchyma and sometimes sclerenchyma in the common tissue known as xylem (Gr. xylo, wood,, based on the fact that wood consists of secondary xylem).This trachea function is to drain water and dissolve essential mineral nutrients, generally from roots to other parts of the plant.  Filter Element (Phloem) Sieve elements are special cells that function in the conduction of products metabolism like sugar. They are usually associated with the parenchyma and are frequent some sclerenchyma in a common tissue known as phloem (Gr. floe, bark, named for the location of the secondary phloem in the inner bark). Sieve elements are elongated cells that have only a primary wall without lignified secondary cell walls. This primary wall has specialized pores , which are collected together into sieve areas. Each pore of the sieve area is a continuous hole in the cell wall primer coated with a substance called callose, a polysaccharide consisting of -1,3-glucose units. The sieve elements are "semi-alive" at maturity which means that these cells are missing the nucleus and other organelles but maintains the endoplasmic reticulum, mitochondria, and plastids. Like tracheal elements, sieve elements oriented end to end, forming a canal like a tube.