for a like purpose. Some; time afterwards the park was
ploughed up, and the broom became, generally spread over
it. Some years ago,-a gentleman planted a garden in Stirlingshire,
and as he was about- to make a washing-green in
the immediate neighbourhood, he took from six* to nine
inches of soil off the surface of the field, and carried it into
the garden : he then sowed the washing-green, with graSs-
seeds. In the field thus uncovered seedling' broom appeared
as thick as the grass which had been sown. Broom is a: frequent
plant throughout the whole district in which the king’s
park and this gentleman's garden are situated, but the seeds
could not have been supplied by the wind, as Professor Graham
concludes, from th e . following reasons: first, because
they are heavy, round, and without wings; and, secondly,
because all the broom-seed in the parish could not have: produced
such a crop, as that which sprang up in the said
bleaching-ground. : How long the seeds must have remained
in the ground cannot even be conjectured ; no cause can.be
. imagined which can have conveyed them within many years
either to the king’s park, or the bleaching g ground. The
fact cannot be attributed to the agency of winds for i the reasons
above stated, and the form of the ground 'Is $uch, that
no stream of water could have transported them, or have
covered them afterwards with soil. Such an .effect must have
resulted from the operation of causes continued during a lo n g
period of time.
In several places in the neighbourhood of Edinburgh, th e
breaking of the surface, as Professor Graham assures me,
produces an abundant crop of Fumaria Parviflora, although
the same plant had never before been observed in the neighbourhood.
A gentleman near Dumfries lately cut in a steep bank a
new approach to his house, and immediately a large quantity
of Verbascum Thapsus sprang up.
Another fact of a similar kind, which I likewise owe to.Dr.
Graham, would serve to indicate, if there were any doubt
on the subject, what is the true explanation of the preceding.
“ To the westward of Stirling there is a large peat-bog, a
great part of which has been flooded away by raising wafer
from the river Teith and discharging it into the Forth, the
under-soil. of clay-being then cultivated. The clergyman of
the parish standing by while the workmen were forming a
ditch in -ttSs clEiy/which, had. been covfered.with fourteen feet
of peat-earth,- saw someiseeds in the; clay which) was thrown
out of the ditch he;t©ok;some of them up and.sowed them;
they germinated and produced a.'Crap of Chrysanthemum
Septum. What a period of yea-rS/musti have elapsed while
the seeds were getting their covering; of clay,, and. while this
clay beekrtie buried under fourteen feet of peat-earth!
These facts, which clearly prove that seeds may be concealed
in the earth for ant indefinite period without; losing
their vitality,’ must have an important bearing on the theory
tff the dispersion of plants. ^They-show that there i&stto necessity
for resorting to so bold an hypothesis, as that of equivocal
production, in examples which would be otherwise very
difficultrof explanation. |
To return, to .the consideration of the diffusibility of seeds
by means of ^atmospheric > currents) it eannot.be doubled, that
their agency is productive of considerable effects in the dispersion
of it^e lighter seeds, such as those, of 'mosses, fungi,
anddichens ,; these are diffusible through&the. air in an impalpable
powder, like thin smoke, which may be blown to very
distant places, arid under the influence of permanent aerial
currents, such as s" the trade-winds, .may be conveyed), as it
would appear very probable, from one part of the world to
another. M. De Candolle; has recorded an observation, which
seems to place this supposition-beyond all reasonable doubt.
At Quimper Corentin, on the south-west coast of Britanny, he
discovered on some trees two; lichens; the sticta. crocata and
the physcia flavicans,. which have never, been.found in any
place in France. These lichens are peculiar to Jamaica, and
M. De Candolle supposes that their seeds had been carried
thence by the south-westerly winds, which prevail during a
great part of the year on this part of the French coast.*
* Essai sür la Geographie Botanique.