Manna, a concrete saccharine exudation obtained by making transverse incisions into the stems of cultivated trees of Fraxinus Ornus. The manna ash is cultivated chiefly in Sicily and Calabria for the purpose of obtaining manna. In July or August the collectors make deep cuts through the bark to the wood near the base of the tree; and if the weather be warm and favourable, the manna begins to ooze out of the cuts slowly, and hardens in lumps or flakes, which are from time to time removed by the collectors. Manna is a light porous substance, usually in stalactiform pieces, 1 to 6 inches long, crystalline, friable, yellowish in colour, with a honey-like odour and a sweetish, somewhat bitter taste. It is used in medicine as a gentle purgative for young children. It consists of about 60 to 80 per cent. of mannite, about 10 per cent. moisture, a bitter substance, and other less important constituents. There are several other manna-yielding plants besides the ash, especially the manna-bearing Eucalyptus of Australia (Eucalyptus mannifera), which is non-purgative, and is a favourite sweetmeat with the children of that country. Small quantities are found on the common larch in some districts; this kind is known under the name of manna of Briançon.
The manna of the Israelites, which they ate during their wanderings in the wilderness, was identified by Ehrenberg with the saccharine substance called Mount Sinai Manna, which is produced in that region by a shrub, Tamarix mannifera, a species of Tamarisk (q.v.), from the branches of which it falls to the ground. It does not, however, contain any mannite, but consists wholly of mucilaginous sugar. The exudation which concretes into this manna is caused by the punctures made in the bark by insects of the genus Coccus (C. manniparus), which sometimes cover the branches. It is a kind of reddish syrup, and is eaten by the Arabs and by the monks of Mount Sinai like honey with their bread. Others have supposed that the manna of the Jews was produced by a species of Camel's Thorn (q.v.).