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 original mother plant used to produce the first explants is susceptible to a pathogen or environmental condition, the entire crop would be susceptible to the same problem. Conversely, any positive traits would remain within the line also. Plant tissue culture is used widely in the plant sciences, forestry, and in horticulture. Applications include: Although some growers and nurseries have their own labs for propagating plants by the technique of tissue culture, a number of independent laboratories provide custom propagation services. The Plant Tissue Culture Information Exchange lists many commercial tissue culture labs. Since plant tissue culture is a very labour-intensive