Hemiptera plant. Phloem sap, which has a higher concentration of sugars and nitrogen, is under positive pressure unlike the more dilute xylem sap. Most of the Sternorrhyncha and a number of Auchenorrhynchan groups feed on phloem. Phloem feeding is common in the Fulgoromorpha, most Cicadellidae and in the Heteroptera. The Typhlocybine Cicadellids specialize in feeding on non-vascular mesophyll tissue of leaves, which is more nutritious than the leaf epidermis. Most Heteroptera also feed on mesophyll tissue where they are more likely to encounter defensive secondary plant metabolites which often leads to the evolution of host specificity. Obligate xylem feeding is a
Plant tissue culture they are preferred in several regeneration systems for micropropagation, ploidy manipulation, gene transfer, and synthetic seed production. Nonetheless, tissue regeneration via organogenesis has also proved to be advantageous for studying regulatory mechanisms of plant development. The tissue obtained from a plant to be cultured is called an explant. Explants can be taken from many different parts of a plant, including portions of shoots, leaves, stems, flowers, roots, single undifferentiated cells and from many types of mature cells provided are they still contain living cytoplasm and nuclei and are able de-differentiate and resume cell division. This has given rise to the