the equator. But what is a 'tree limit'?"

"Don't you remember, little girl," answered the Doctor, "what I told you
about the timber-line on a mountain--the height beyond which no trees
grow, because it gets too cold for them up there? It is just the same if
you go northward on flat ground like Orchard Farm; for when you have
gone far enough there are no more trees to be seen. In that northern
country the winter is so long and cold, and summer is so short, that
only scrubby bushes can grow there. Next beyond these we should find
merely the rough, curling grass of the Barren Grounds, which would tell
us we were approaching the arctic circle, and already near the place
where wise men think it is best to turn homeward; for it is close to the
Land of the Polar Bear and the Northern Lights--the region of perpetual
snow. But dreary as this would seem to us, nest building is going on
there this June day, as well as here.

"Running lightly over uneven hummocks of grass are plump, roly-poly,
black-and-white birds, with soft musical voices and the gentlest
possible manners. They may have already brought out one brood in thick,
deep grassy nests, well lined with rabbit fur or Snow Owl feathers, that
they know so well how to tuck under a protecting ledge of rock or bunch
of grass. Now and then a male Snowflake will take a little flight and
sing as merrily as his cousin the Goldfinch, but he never stays long
away from the ground where seeds are to be found.

"The white feathers of these birds are as soft as their friend the snow,
of which they seem a part. They have more white about them than any
other color, and this snowy plumage marks them distinctly from all their
Sparrow cousins. After the moult, when a warm brown hue veils the white
feathers, and the short northern summer has ended, the birds flock
together for their travels. When they will visit us no one can say; they
come and go, as if driven by the wind.

"A soft clinging December snowstorm begins, and suddenly you will wonder
at a cloud of brown, snow-edged leaves that settle on a bare spot in the
road, then whirl up and, clearing the high fence, drop into the shelter
of the barnyard.

"'How very strange,' you will say; 'these leaves act as if they were
bewitched.' You look again, and rub your eyes; for these same whirling
winter leaves are now walking about the yard, picking up grass-seed and
grain under the very nose of the cross old rooster himself! Then you
disc