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Decay (xylem) Trametes versicolor = Coriolus versicolor. Flammulina velutipes Ganoderma applanatum = Fomes applanatus Phellinus spp. = Fomes spp. Pleurotus spp. Polyporus squamosus Other basidiomycetes Discoloration (xylem) Deuteromycetes Dothiorella canker and wilt Dothiorella ulmi: Dutch elm disease Ophiostoma ulmi = Ceratocystis ulmi
In the stems of some Asterales dicots, there may be phloem located inwardly from the xylem as well. Between the xylem and phloem is a meristem called the vascular cambium. This tissue divides off cells that will become additional xylem and phloem. This growth increases the girth of the plant, rather than its length. As long as the vascular ...
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts of the plants such as stems and leaves, but it also transports nutrients .
Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve-tube elements. [citation needed] The xylem consists of vessels in flowering plants and of tracheids in other vascular plants. Xylem cells are dead, hard-walled hollow cells arranged to form files of tubes that function in water transport.
Because phloem tubes are located outside the xylem in most plants, a tree or other plant can be killed by stripping away the bark in a ring on the trunk or stem. With the phloem destroyed, nutrients cannot reach the roots, and the tree/plant will die.
Like all vascular plants, trees use two vascular tissues for transportation of water and nutrients: the xylem (also known as the wood) and the phloem (the innermost layer of the bark). Girdling results in the removal of the phloem, and death occurs from the inability of the leaves to transport sugars (primarily sucrose) to the roots.
Once a plant is infected, the bacteria spread through the xylem vessels from the area of infection to the main stem, and the entire plant wilts and dies. Initial symptoms may include the wilting of single leaves and smaller stems. Infected plants may produce a creamy white bacterial ooze when cut.
Before the molecular era, the diagnosis of diseases caused by phytoplasma was difficult because the organisms could not be cultured. Thus, classical diagnostic techniques, including symptom observation, were used. Ultrathin sections of phloem tissue from plants with suspected phytoplasma-infections were also studied. [3]