Thoreau writes in his journal:
Part of the white maples now begin to flow, some perhaps two or three days. Probably in equally warm positions they would have begun to flow as early as those red ones which I have tapped. Their buds, and apparently some of the red ones, are visibly swollen . . .
At the red maple which I first tapped, I see the sap still running and wetting the whole side of the tree . . .