Exodus 16:15 - Albert Barnes' Notes on the Bible

It is manna - “Man” or “man-hut,” i. e. white manna, was the name under which the substance was known to the Egyptians, and therefore to the Israelites. The manna of the Peninsula of Sinai is the sweet juice of the Tarfa, a species of tamarisk. It exudes from the trunk and branches in hot weather, and forms small round white grains. In cold weather it preserves its consistency, in hot weather it melts rapidly. It is either gathered from the twigs of tamarisk, or from the fallen leaves underneath the tree. The color is a greyish yellow. It begins to exude in May, and lasts about six weeks. According to Ehrenberg, it is produced by the puncture of an insect. It is abundant in rainy seasons, many years it ceases altogether. The whole quantity now produced in a single year does not exceed 600 or 700 pounds. It is found in the district between the Wady Gharandel, i. e. Elim, and Sinai, in the Wady Sheikh, and in some other parts of the Peninsula. When therefore the Israelites saw the “small round thing,” they said at once “this is manna,” but with an exclamation of surprise at finding it, not under the tamarisk tree, but on the open plain, in such immense quantities, under circumstances so unlike what they could have expected: in fact they did not know what it really was, only what it resembled.