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INTEODUCED PLANTS IN WEST CORNWALL.
By W. Roberts.
The plants in the following list nearly all occur, or have
occurred, within a few yards of one another on a barren piece of
ground known as the Eastern Green, which borders the railwaycutting
between Penzance and Marazion, and fringes the beach.
Within a mile, in a direct line inland, is situated an extensive flour
mill, which receives large cargoes of wheat from ports in America,
from Dantzic, from the Black Sea and the Sea of Azov, and from
Egypt and India. As the corn is winnowed on the Eastern Green,
and as in the nature of things it inevitably contains a greater or
lesser percentage of the seeds of various weeds, it is only natural
that some of this "chaff" falls on su.itable soil and springs into
growth.
In most cases their life is brief, and in very few instances do
they appear a second year. They rarely give one the impression
of being typical specimens. The climate in the first place, the
station in the second, and the fact that the ground is already
densely occupied with vegetable growth of a vigorous character in
the third, are fatal elements to the acclimatisation of weakly corn-
field denizens. The plants in question appear, for the most part,
to thrive only under special circumstances, although the geographical
distribution of nearly every one is wide. DeCandolle, in
his ' Geographie Botanique Raisonnee,' tells us that it is not so
much a total annual average amount of heat that a plant requires
to enable it to vegetate, to flower, or to ripen its seed, as that this
heat shall never descend below or ascend above certain extremes,
and that it shall remain within those limits for a sufficient length
of time for the completion of these operations, a period of time
which may be shortened or lengthened according to the greater or
less intensity of the heat received by the plant within the above
limits. This exactly defines the position of the colony of additions
to the Flora of West Cornwall. The absence of extremes—heat
and cold—is fatal to their welfare. It is also an interesting fact to
note that nearly the whole of these additions are normally of
annual duration, so that the chances are materially increased
against self-propagation.
I am indebted to a local botanist, Mr. W. A. Glasson, for a
complete list, and also for specimens : the names have been verified
by Mr. N. E. Brown. The "Eastern Green" and the neighbourhood
which terminates at one point with the Marazion marshes is
peculiarly rich in its flora, and during the past half-century the
late John Ralfs noticed and recorded the names of several plants
to which, regarding as aliens, he paid very little attention. Mr.
Glasson began his observations in the summer of 1885, when he
found Sap'inaria Vaccaria, which had been observed near the Logan
Rock ui 1878 by Dr. Eraser ; the next species, which had also been
observed before, was Erhinoxpennum Lappidn, and, finding these two
plants, Mr. Glasson was led to pay close attention to the district.