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the latter are particularly useful, they speedily cover
the earth and stones, and keep the surface in that state
of moisture which is so very advantageous. All kinds
of grasses, on the contrary, should be exterminated,
for they are of so rapid a growth, and vigorous a
nature, that they quickly overpower, weaken, and
finally destroy the more delicate among the Ferns.
There is one species, Trichomanes speciosum, which
in a state of nature has its fronds always wet; it
invariably grows within the spray of waterfalls, or in
similar situations, where it is constantly supplied with
the needful moisture. This I find a most difficult
situation to imitate, but it may be managed by suspending
above the Fern a vessel containing water,
which shall be allowed to drop slowly on a stone, or
other hard substance in the neighbourhood of the
plant, the fronds of which will be wetted by the
sprinkling caused by each drop. Polypodium
Phegopteris and Cystopteris fragilis benefit greatly
by a similar treatment.
There is one Fern, Asplénium marinum, which
hitherto I have failed to cultivate in anything like its
natural luxuriance ; this species grows on the most
exposed rocks on our bleakest shores, and yet I
believe it has never been cultivated in the open air
with success : in a temperature of 70“ Fah. it will
grow with vast rapidity ; and with a lower temperature,
with artificial protection, it also answers very well.
Adopting this plan of cultivation, I have possessed the
opportunity of observing the changes that took place.
and of watching, as it were, the progress of variation.
I have pressed fronds from the same root for three
successive years, and have found variations abundantly
adequate to the establishment of species quite
as distinct as many of those in the English Flora;
and I consider all that cultivation, as I have explained
it, can accomplish for any plant is, to hasten or delay
those changes to which that plant is by nature liable :
it cannot increase or diminish the number of actual
species. In those species liable to great extremes in
the cutting of their fronds, I have observed that a soil
composed of decaying wood, abundantly supplied,
and completely covering the roots, hastens a development
of the most divided form which they can possibly
assume; while a mixture of sand and stones,
and a deficiency even of these, retards the development,
and not unfrequently causes the plant to return
to a more simple form.
Besides the British Ferns, all the species indigenous
to the northern regions of America, Europe, and
Asia may be grown in the open air, and without protection,
excepting from severe frost, when they
should be covered with straw, matting, or dried tan,
thus supplying that warm clothing of snow which
protects them from extreme cold in their native
habitats. But if we advance one step, and restrain
the free communication with the outer air, then there
seems to be no hmit to the species we may introduce—•
the beautiful productions of the tropics may be
brought to our doors.