Vascular Bundle

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In Botany , in plants with life cycle diplonte haplotypes (ie, individuals with generations alternating haploid and diploid ), is called the gametophyte generation of the individual haploid . The gametophyte is a descendant of an adult fertile diploid generation (sporophyte called), and in turn will also be direct descendants diploid (sporophyte).
The gametophyte is initially a single haploid cell resulting from meiosis produced in the sporophyte (diploid multicellular individual adult), but unlike what happens to animals for example, the haploid cell then develops by mitosis , giving a multicellular adult individual. Multicellular adult is this which will give the gametes fertile will join during fertilization , giving a new diploid individual.
The gametophyte produces gametes male or female (or both). No change in number of chromosomes in the gamete, which has the same number of chromosomes haploid gametophyte and that therefore in this case the gametes are produced by mitosis (ie a difference with what happens in the life cycle diplonte animals possess, for example). The fusion of male and female gametes produces ...
... the zygote diploid .
In the mosses ( Bryophyta sensu lato ) and the ferns and their allies , the gametophyte is a visible phase of the life cycle. In bryophytes the gametophyte is said is "the dominant phase" of the life cycle, it is photosynthetic and must resist the selection pressure of the environment. However in other land plants the gametophyte is very small (as in ferns ) or seed plants ( Spermatophyta ), where the embryo sac is known as megagametophyte and the male form ( pollen ) is called microgametofito .
When the life cycle of a plant multicellular haploid generation is not (hence diplonte possess a cycle similar to that of animals) says it has no gametophyte.

In botany , a vascular bundle is each of the individual cords forming the primary vascular system of plants . It is an assembly of vascular tissues, xylem and phloem , sometimes including associated mechanical tissue ( parenchyma and sclerenchyma ).
The primary vascular tissues are formed from the procambium . Both the xylem and phloem consist of two parts that take place one after another: proto and metaxylem and proto and metaphloem. The protoxylem consists of tracheids ringed or spiral, which eventually stretched and destroyed. The metaxylem is more complex, can have reticulated and dotted vessels and fibers, is the only conducting tissue of plants that have no secondary growth. The mature protophloem the plant parts which are extending, most cells are parenchyma, its elements are obliterated and crush soon. The metaphloem has sieve elements with companion cells, parenchyma cells as well. In plants without secondary growth, phloem is the only adult organs.
The phloem and xylem show variations in relative position, determining different types of vascular bundles.
Make collateral. Phloem is located on the outer side or abaxial beam, while the xylem is located on the inner side or adaxial. It is most common in angiosperms and gymnosperms . The collateral bundles are of two types:
It closed side. In most pteridophytes , monocots and dicots forbs, not retain the vascular procambium after primary vascular tissues reach the adult stage. Hence lack of capacity for further growth. The protoxylem tracheary elements stretch and eventually destroyed. In the vascular bundles of many grasses (grasses) protoxylem destruction leads to the formation of an open space called protoxilemática lagoon .
Ask open side. Most dicots and gymnosperms have open beams, with a persistent vascular meristem between the xylem and phloem: the cambium bundle, which is formed from a remnant of procambium.
Make bicolateral. The beams have bicolaterales phloem on both sides of the xylem, outward and inward. They are found in species of some families of dicots, such as convolvulus , Apocynaceae , Solanaceae , Cucurbitaceae and milkweed and some tribes of Asteraceae (composites). The fascicular cambium is located between the xylem and phloem outside and there is also a cambium between the xylem and internal phloem. In the internal phloem bundles bicolaterales differs after the external, and their differentiation is centrifugal.
Ask concentric. In concentric bundles, one of the vascular tissues completely surrounds the other. Concentric beams are closed. The beam is called perixilemático or anfivasal if the xylem surrounds the phloem, this type of beam is found in many monocots, the medullary bundles of some dicots are also of this type. If the phloem surrounding the xylem, the beam is perifloemático or anficribal . They are common in pteridophytes and angiosperms flowers and fruits.

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