seemingly been to hit upon some new theory of distribution. The "bird
theory" is a failure, as we have shown; nor do they invariably fly due
east or west, so as to supply the several climatic zones with their
respective vegetations. The same is true of the "squirrel theory," for
this nimble little rodent is as likely to head north or south as to follow
the course of the sun; the "wind theory" is subject to too many shifts and
changes to be accounted a reliable agency; the "river-and-ocean-current
theories" are still less satisfactory, since rivers flow in diverse
directions, and ocean currents bear with safety only their own aquatic
plants; the "mummy-case theory" is hardly an accredited agency, and the
"war theory" is attended with too much destruction of life to be safely
relied on as conserving the vital forces of nature. The climatic zones,
and high and low altitudes, have still to be consulted to get at the real
causes of distribution, or such as conclusively satisfy the scientific
mind. For no single plant is really a cosmopolite. They are simply the
habitats of their own separate zones, except as high altitudes are
reached, and climatic and other conditions favor the appearance of such
vegetation as belongs to other plant zones. If we would find the more
common plants and weeds of New England in North Carolina or Tennessee, we
must go into the mountainous regions of those states, at an altitude which
compensates for the difference in latitude, and where the influencing
conditions of plant-life are essentially the same. In such localities, we
shall find the same household plants, garden weeds, and general
vegetation, as in higher northern latitudes, not because their seeds have
been borne thither from New England or elsewhere, but because the same
climatic, telluric and other conditions prevail as in the more northern
localities. And these conditions are what determine the development and
growth of local vegetations.

And so of the alpine firs, grasses, harebells, lichens, mosses, etc. Their