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STUDIES IN PH LE UM ARENARIUM
383
p. 928) are indicated as »päturages sablonneux dans les clairières des
forèts de montagnes, 1,400—2,000 ni».
The bricf statements in botanical papers both as regards Central
Europé and the Mediterranean Area otherwise agree in the main as to
the appearance of the species. In general, sandy fields near the
sea-shores and dunes are stated as being the most important types of
habitat. As to the frequencv of this species different authors varv
considerablv in their statements probably partly depending ön those
regionallv important variations as regards the degree of frequency
which have been stated previously, but also partly because the
bounda-ries between the frequency degres in different papers are fixed in
different ways.
The few precedent examples ön the ecology of Piil. arenarium,
chosen out of the literature, have made il quite clear that our species
is a pronounced psammophyte. Sandy areas, however, are also found
in the interiör parts of Europé to a certain extent and the psammophility
of the species alone will not explain its confinement to the vicinity of
the sea-shores. The decisive point in this case is that the distribution
is not merely checked bv the appearance of drifting, dune-forming
sand hut also by a high Ca-standard in the soil and by the presence
of an oceanic climate, in which perhaps the mild winters play a
parti-cularly important röle (cf. Massart 1912, p. 107).
The map of the total distribution shows some rather good examples
regarding the Cooperation of the above-named factors. That the
distribution shows gaps in parts of eu-oceanic Western Europé often seems
to be caused by the lack of suitable sandy localities (e.g. the southern
coast of the Bay of Biscay, parts of the coast of Scotland. Brittany).
Ön the other liand it is shown that dune areas like those between Rügen
and Danzig, so particularly well suited for Piil. arenarium, present no
localities of this kind. probably due to the climate. which in those
dislricts seems to exceed the degree of continentality above which this
species can find no constant growth.
Thus, the distribution of our species seems in general lo be
occa-sioned and explained by now active and measurable factors, partly
edafic — chemical and mechanical composition of the soil - and
partly atmospheric — presence of an oceanic tvpe of climate. Further,
wi th in the whole distribution area of the species phytobiotic factors
seem lo play a certain röle — slight competitive power. Finally, in
the furthest radiations to the north (perhaps also in those to the south?)
anthropogenic factors are active — the species’ hemerophility.
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