the frost drew it down; and an excess of either stops the flow. Before
the sun has got power to unlock the frost, there is no sap; and after
the frost has lost its power to lock up again the work of the sun,
there is no sap. But when it freezes soundly at night, with a bright,
warm sun next day, wind in the west, and no signs of a storm, the veins
of the maples fairly thrill. Pierce the bark anywhere, and out gushes
the clear, sweet liquid. But let the wind change to the south and blow
moist and warm, destroying that crispness of the air, and the flow
slackens at once, unless there be a deep snow in the woods to
counteract or neutralize the warmth, in which case the run may continue
till the rain sets in. The rough-coated old trees,--one would not think
they could scent a change so quickly through that wrapper of dead, dry
bark an inch or more thick. I have to wait till I put my head out of
doors, and feel the air on my bare cheek, and sniff it with my nose;
but their nerves of taste and smell are no doubt under ground, imbedded
in the moisture, and if there is anything that responds quickly to
atmospheric changes, it is water. Do not the fish, think you, down deep
in the streams, feel every wind that blows, whether it be hot or cold?
Do not the frogs and newts and turtles under the mud feel the warmth,
though the water still seems like ice? As the springs begin to rise in
advance of the rain, so the intelligence of every change seems to
travel ahead under ground and forewarn things.

A "sap-run" seldom lasts more than two or three days. By that time
there is a change in the weather, perhaps a rainstorm, which takes the
frost nearly all out of the ground. Then, before there can be another
run, the trees must be wound up again, the storm must have a white
tail, and "come off" cold. Presently the sun rises clear again, and
cuts the snow or softens the hard-frozen ground with his beams, and the
trees take a fresh start. The boys go through the wood, emptying out