ants
employing insects to carry pollen from one to another feel superior to
the wind-fertilised clan. We may fancy the duckweed (speaking of the
pine) to say: "Of course, he is very big and of an ancient family, but
for that very reason he is primitive in his habits. I know he boasts
that he employs the winds of heaven as marriage priests, but we are
served by the animal kingdom in our unions--and that, you must allow, is
something to be proud of." {6} But duckweeds grow so crowded together
that they are probably fertilised, to a great extent, by contact with
their neighbours, without aid from the animal kingdom. We may also
imagine the duckweed reproving the pine for his extravagance in the
matter of pollen production. This, however, is necessary, because the
pollen being sown broadcast by the wind, it is a matter of chance whether
or not a grain reaches the stigma of its own species, and the chance of
its doing so is clearly increased by multiplying the number of
pollen-grains produced. Enormous quantities of the precious dust are
wasted by this prodigality. We read of pollen swept from the decks of
ships, or coating with a yellow scum lakes hidden among Tyrolean
pinewoods. Pollen is so largely dispersed in the air that it has been
supposed to be a cause of hay-fever.

Blackley found, by means of a sticky plate, which could be exposed and
covered again, when raised high in the air on a kite, that pollen is
dispersed to considerable altitudes. Wherever vegetable _debris_
collects, pollen-grains may be found. Kerner found them, together with
wind-borne seeds and scales of butterflies' wings, sticking to the ice in
remote Alpine glaciers.

Another characteristic of wind-borne pollen is dryness or dustiness; the
grains are smooth, not sculptured like the pollen meant to be carried by
insects; nor are they sticky or oily, as is often the case with
entomophilous pollen. The advantage to the plan is obvious; the grains,
from the absence of the burr-like quality, or of any other kind of
adhesiveness, do not tend to hold together in clumps, but separate easily
from one another, and float all the more easily. {7}

Several adaptations are found to favour the dispersal of the pollen.
Wind-fertilised plants are generally tall; thus in Europe, at least, the
commonest representatives of the class are shrubs or trees--witness the
fir-trees, yew, juniper, oak, hazel, birch. And where the plants are
lowly--_e.g._, grasse