this because they lack two adaptations that are necessary to enable direct use by animals. These include the existence of a very high ratio of non-essential/essential amino acids in phloem sap for which these adapted Hemiptera insects contain symbiotic microorganisms which can then provide them with essential amino acids; and also insect "tolerance of the very high sugar content and osmotic pressure of phloem sap is promoted by their possession in the gut of sucrase-transglucosidase activity, which transforms excess ingested sugar into long-chain oligosaccharides." A much larger set of animals do however consume phloem sap by proxy, either "through feeding on the honeydew of phloem-feeding hemipterans. Honeydew is physiologically less extreme than phloem sap, with a higher essential/non-essential amino acid ratio and lower osmotic pressure," or by feeding on the biomass of insects that have grown on more direct ingestion of phloem sap. Human uses Maple syrup is made from reduced sugar maple xylem sap. The sap often is harvested from the sugar maple, Acer saccharum. In some countries (e.g., Lithuania, Latvia, Estonia, Finland, Belarus, Russia) harvesting the early spring sap of birch trees (so called "birch juice") for human consumption is common practice; the sap can be used fresh or fermented and contains xylitol. Certain palm tree sap can be used to make palm syrup. In the Canary Islands they use the Canary Island date palm while in Chile they use the Chilean wine palm to make their syrup called miel de palma. See also Latex Resin References External links Plant physiology Trees Tree tapping