The Botany of Iceland - 01.12.1930, Side 149

STUDIES ON THE VEGETATION OF ICELAND
139
species belongs, it applies to all species that there is
one class of moisture in which the species attains its
highest F.-percentage and shortest distance between the
individuals, and outside which the F.- percentage de-
creases and the distance between the individualfe in-
creases whether we go up or down the scale of moisture.
The distribution of the species in the scale may afford ground
for the setting up of a series of types characterised by the magnitude
of the F.-percentage, the position of the maximum in the scale, the
number of classes in which tlie species occurs etc. etc., and in time
it will be necessary to introduce a terminology in order to charac-
terise hriefly the relations of a species within an area. At the present
lime, while such investigations are still in their inception, there is
no reason to set up such a system, especially since a good deal of
material would be requisite for such a purpose. This part of the
investigation must therefore be left uritil a iater period. In this
connection it will suffice, as was the main object of our investiga-
tion, to establisli the fact tliat a species is closely identified
with a definite degree of moistureofthesoil. If there is
any change in the degree of moisture, no matter in what direction,
the F.-percentage of the species will change simultaneously, and the
greater the cliange in the degree of moisture, the greater, too, will be
the change in the F.-percentage, until such conditions of moisture
are reached as entirely exclude the species. The species reacts
identically to clianges in moisture wherever it occurs.
The table shows how markedly this is the case in the three
localities Bjork, Lýngdalur, and Arnarvatnsheiði therein indicated.
These three localilies have been selected at random from the areas
of distribution of the species discussed, and there is no reason to
suppose that an investigation in other localities under the same
external conditions would give a picture of the relation of the species
concerned to the degree of moisture essentially different from that
shown in the table. Greater certainty might of course be gained by
an increased nurnber of investigations, in that the influence on the
magnitude of the F.-percentage of accidental factors, i. e. faclors
not determined by the degree of moisture, would be precluded or
diminished.
The distribution of a species in a scale.of external
íactors is just as constant and »good« a character in a
species as anjr morphological or anatomical character.